Carbazole Compound, Light-Emitting Element Material, Organic Semiconductor Material, Light-Emitting Element, Light-Emitting Device, Lighting Device, and Electronic Device

ABSTRACT

An object is to provide a novel carbazole compound that can be used for a transport layer, a host material, or a light-emitting material in a light-emitting element. A carbazole compound where nitrogen of a carbazole group, the carbazole skeleton of which whose 3-position is bonded to the 4-position of a dibenzofuran skeleton or a dibenzothiophene skeleton, is bonded to a benzimidazole skeleton through a phenylene group, is provided. The carbazole compound has a high carrier-transport property, and can be suitably used for a material for a light-emitting element or for an organic semiconductor material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a carbazole compound that can be usedfor a light-emitting element material. The present invention furtherrelates to a light-emitting element material, an organic semiconductormaterial, and a light-emitting element each using the carbazolecompound.

2. Description of the Related Art

As next generation lighting devices or display devices, display devicesusing light-emitting elements (organic EL elements) in which organiccompounds are used as light-emitting substances have been developed atan accelerated pace because of their advantages of thinness,lightweightness, high speed response to input signals, low powerconsumption, etc.

In an organic EL element, voltage application between electrodes,between which a light-emitting layer is interposed, causes recombinationof electrons and holes injected from the electrodes, which brings alight-emitting substance into an excited state, and the return from theexcited state to the ground state is accompanied by light emission.Since the wavelength of light emitted from a light-emitting substance ispeculiar to the light-emitting substance, use of different types oforganic compounds as light-emitting substances makes it possible toobtain light-emitting elements which exhibit various wavelengths, i.e.,various colors.

In the case of display devices which are expected to display images,such as displays, at least three-color light, i.e., red light, greenlight, and blue light is necessary for reproduction of full-colorimages. Further, in application to lighting devices, light havingwavelength components uniformly in the visible light region is ideal forobtaining a high color rendering property, but in reality, lightobtained by mixing two or more kinds of light having differentwavelengths is used for lighting application in many cases. It is knownthat, with a mixture of three-color light, i.e., red light, green light,and blue light, white light having a high color rendering property canbe obtained.

Light emitted from a light-emitting substance is peculiar to thesubstance, as described above. However, important performances as alight-emitting, element, such as lifetime, power consumption, and evenemission efficiency, are not only dependent on a light-emittingsubstance but also greatly dependent on layers other than alight-emitting layer, an element structure, properties of an emissioncenter substance and a host material, compatibility between them,carrier balance, or the like. Therefore, it is true that many kinds oflight-emitting element materials are necessary for the growth of thisfield. For the above-described reasons, light-emitting element materialswith a variety of molecular structures have been proposed (e.g., seePatent Document 1).

As is generally known, the generation ratio of a singlet excited stateto a triplet excited state in a light-emitting element usingelectroluminescence is 1:3. Therefore, a light-emitting element in whicha phosphorescent material capable of converting the triplet excitedstate to light emission is used as an emission center substance cantheoretically realize higher emission efficiency than a light-emittingelement in which a fluorescent material capable of converting thesinglet excited state to light emission is used as an emission centersubstance.

However, since the triplet excited state of a substance is at a lowerenergy level than the singlet excited state of the substance, asubstance that emits phosphorescence has a larger band gap than asubstance that emits fluorescence when the emissions are at the samewavelength.

As a substance serving as a host material in a host-guest typelight-emitting layer or a substance contained in each transport layer incontact with a light-emitting layer, a substance having a larger bandgap or higher triplet excitation energy (energy difference between atriplet excited state and a singlet ground state) than an emissioncenter substance is used for efficient conversion of excitation energyto light emission from the emission center substance.

Therefore, a host material and a carrier-transport material each havinga further larger band gap or higher triplet excitation energy arenecessary in order that fluorescence at a shorter wavelength than bluefluorescence or phosphorescence at a shorter wavelength than greenphosphorescence be efficiently obtained. There are however not manyvariations of materials that have a sufficiently large band gap or hightriplet excitation energy in addition to good characteristics as alight-emitting element material, and as described above, the performanceof a light-emitting element depends also on the compatibility betweensubstances. In consideration of the above, it is difficult to say thatthere are sufficient variations of materials with which light-emittingelements having good characteristics can be manufactured.

REFERENCE

-   Patent Document 1: Japanese Published Patent Application No.    2007-15933

SUMMARY OF THE INVENTION

Therefore, an object of one embodiment of the present invention is toprovide a novel carbazole compound that can be used for a transportlayer, a host material, or a light-emitting material in a light-emittingelement.

Another object of one embodiment of the present invention is to providea light-emitting element material using the above novel carbazolecompound.

Another object of one embodiment of the present invention is to providean organic semiconductor material using the above novel carbazolecompound.

Another object of one embodiment of the present invention is to providea light-emitting element having high emission efficiency.

Another object of one embodiment of the present invention is to providea light-emitting device, a lighting device, or an electronic devicehaving low power consumption. Note that in one embodiment of the presentinvention, it is only necessary that at least one of the above-describedobjects should be achieved.

The present inventors have been able to synthesize a carbazole compoundwhere nitrogen of a carbazole group, the carbazole skeleton of whichwhose 3-position is bonded to the 4-position of a dibenzofuran skeletonor a dibenzothiophene skeleton, is bonded to a benzimidazole skeletonthrough a phenylene group. Further, the inventors have found out thatthe carbazole derivative has a high carrier-transport property and canbe suitably used for a material of a light-emitting element or for anorganic semiconductor material.

In other words, one embodiment of the present invention is a carbazolecompound where nitrogen of a carbazole group, the carbazole skeleton ofwhich whose 3-position is bonded to the 4-position of a dibenzofuranskeleton or a dibenzothiophene skeleton, is bonded to a benzimidazoleskeleton through a phenylene group. Further, nitrogen at the 1-positionof the benzimidazole skeleton has an aryl group having 6 to 12 carbonatoms.

Note that in the above carbazole compound, carbon in the benzimidazoleskeleton and carbon in the dibenzofuran skeleton or in thedibenzothiophene skeleton may separately have a substituent. When thebenzimidazole skeleton has a substituent, the substituent can be eitheran alkyl group having 1 to 4 carbon atoms or a phenyl group. When thedibenzofuran skeleton or the dibenzothiophene skeleton has asubstituent, the substituent can be either an alkyl group having 1 to 4carbon atoms or an aryl group having 6 to 12 carbon atoms.

Further, the carbazole skeleton in the above carbazole compound may havea substituent at the 6-position, and the substituent can be selectedfrom an alkyl group having 1 to 4 carbon atoms and an aryl group having6 to 12 carbon atoms.

The carbazole compound with such a structure has a highcarrier-transport property and can be suitably used for a host materialor a carrier-transport layer in a light-emitting element. Owing to thehigh carrier-transport property of the carbazole compound, alight-emitting element having low driving voltage can be fabricated.

Further, the carbazole compound has a wide band gap, and therefore canbe suitably used for a host material, into which an emission centersubstance that emits blue fluorescence and fluorescence at a longerwavelength than blue or an emission center substance that emits greenphosphorescence and phosphorescence at a longer wavelength than green isdispersed. Since the carbazole compound has a wide band gap and thushigh triplet excitation energy, the energy of carriers that arerecombined in the host material can be effectively transferred to theemission center substance. Accordingly, a light-emitting element withhigh emission efficiency can be fabricated.

Also for a carrier-transport layer adjacent to a light-emitting layercontaining an emission center substance that emits blue fluorescence oran emission center substance that emits green phosphorescence, thecarbazole compound having a wide band gap can be suitably used withoutdeactivating excitation energy of the emission center substance.Accordingly, a light-emitting element with high emission efficiency canbe fabricated.

The above-described carbazole compound will be more specificallydescribed. One embodiment of the present invention is a carbazolecompound represented by a general formula (G1) below.

In the formula, R¹ to R⁴ separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, a phenyl group, and a tolylgroup, and R⁵ represents an aryl group having 6 to 12 carbon atoms.Further, R⁶ to R¹³ separately represent any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and an aryl group having 6 to 12carbon atoms. In addition, Ph represents a substituted or unsubstitutedphenylene group; when the phenylene group has a substituent, thesubstituent can be an alkyl group having 1 to 4 carbon atoms.Furthermore, X represents a sulfur atom or an oxygen atom.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G2) below.

In the formula, R¹ to R⁴ separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, a phenyl group, and a tolylgroup, and R⁵ represents an aryl group having 6 to 12 carbon atoms.Further, R⁶, R⁷, R⁹, and R¹² separately represent any one of hydrogen,an alkyl group having 1 to 4 carbon atoms, and an aryl group having 6 to12 carbon atoms. In addition, Ph represents a substituted orunsubstituted phenylene group; when the phenylene group has asubstituent, the substituent can be an alkyl group having 1 to 4 carbonatoms. Furthermore, X represents a sulfur atom or an oxygen atom.

The carbazole compound can be synthesized easily.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G3) below.

In the formula, R¹ to R⁴ separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, a phenyl group, and a tolylgroup, and R⁵ represents an aryl group having 6 to 12 carbon atoms.Further, R⁷, R⁹, and R¹² separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, and an aryl group having 6 to 12carbon atoms. In addition, Ph represents a substituted or unsubstitutedphenylene group; when the phenylene group has a substituent, thesubstituent can be an alkyl group having 1 to 4 carbon atoms.Furthermore, X represents a sulfur atom or an oxygen atom.

The carbazole compound is a carbazole derivative having a preferablestructure because the evaporation rate tends to stabilize.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G4) below.

In the formula, R¹ to R⁴ separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, a phenyl group, and a tolylgroup, and R⁵ represents an aryl group having 6 to 12 carbon atoms. Inaddition, Ph represents a substituted or unsubstituted phenylene group;when the phenylene group has a substituent, the substituent can be analkyl group having 1 to 4 carbon atoms. Furthermore, X represents asulfur atom or an oxygen atom.

The carbazole compound can be synthesized inexpensively because of thehigh availability of a material.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G5) below.

In the formula, R⁵ represents an aryl group having 6 to 12 carbon atoms.Further, R⁶ to R¹³ separately represent any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and an aryl group having 6 to 12carbon atoms. In addition, Ph represents a substituted or unsubstitutedphenylene group; when the phenylene group has a substituent, thesubstituent can be an alkyl group having 1 to 4 carbon atoms.Furthermore, X represents a sulfur atom or an oxygen atom.

The carbazole compound can be synthesized inexpensively because of thehigh availability of a material.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G6) below.

In the formula, R⁵ represents an aryl group having 6 to 12 carbon atoms.Further, R⁶, R⁷, R⁹, and R¹² separately represent any one of hydrogen,an alkyl group having 1 to 4 carbon atoms, and an aryl group having 6 to12 carbon atoms. In addition, Ph represents a substituted orunsubstituted phenylene group; when the phenylene group has asubstituent, the substituent can be an alkyl group having 1 to 4 carbonatoms. Furthermore, X represents a sulfur atom or an oxygen atom.

The carbazole compound can be synthesized easily.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G7) below.

In the formula, R⁵ represents an aryl group having 6 to 12 carbon atoms.Further, R⁷, R⁹, and R¹² separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, and an aryl group having 6 to 12carbon atoms. In addition, Ph represents a substituted or unsubstitutedphenylene group; when the phenylene group has a substituent, thesubstituent can be an alkyl group having 1 to 4 carbon atoms.Furthermore, X represents a sulfur atom or an oxygen atom.

The carbazole compound is a preferable evaporation material because theevaporation rate is extremely stable.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G8) below.

In the formula, R⁵ represents an aryl group having 6 to 12 carbon atoms.In addition, Ph represents a substituted or unsubstituted phenylenegroup; when the phenylene group has a substituent, the substituent canbe an alkyl group having 1 to 4 carbon atoms. Furthermore, X representsa sulfur atom or an oxygen atom.

The structure of the carbazole compound can be synthesized inexpensivelybecause of the high availability of a material.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G9) below.

In the formula, Ph represents a substituted or unsubstituted phenylenegroup; when the phenylene group has a substituent, the substituent canbe an alkyl group having 1 to 4 carbon atoms. Further, in the formula, Xrepresents a sulfur atom or an oxygen atom.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G10) below.

In the formula, R⁵ represents an aryl group having 6 to 12 carbon atoms.Further, R⁷, R⁹, and R¹² separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, and an aryl group having 6 to 12carbon atoms. Furthermore, X represents a sulfur atom or an oxygen atom.

The carbazole compound has a high carrier-transport property.

Another structure of the present invention is a carbazole compoundrepresented by a general formula (G11) below.

In the formula, X represents a sulfur atom or an oxygen atom.

Another embodiment of the present invention is a carbazole compoundrepresented by the following structural formula.

Another embodiment of the present invention is a carbazole compoundrepresented by the following structural formula.

Another structure of the present invention is an organic semiconductormaterial containing any of the above carbazole compounds.

Another structure of the present invention is a light-emitting elementincluding a layer containing an organic compound between a pair ofelectrodes, in which light emission is obtained from the layercontaining an organic compound by voltage application between theelectrodes and the layer containing an organic compound contains any ofthe above-described carbazole compounds.

Another structure of the present invention is a light-emitting deviceincluding the above light-emitting element and a means for controllingthe light-emitting element.

Another embodiment of the present invention is an electronic deviceincluding the above light-emitting device.

Another structure of the present invention is a lighting deviceincluding the above light-emitting element.

A carbazole compound having any of the above-described structures is asubstance having both an excellent carrier-transport property and a wideband gap, and can be suitably used for a material included in atransport layer or a host material or an emission center substance in alight-emitting layer for a light-emitting element. A light-emittingelement using a light-emitting element material including the carbazolecompound can be a light-emitting element having high emissionefficiency. In addition, a light-emitting element using a light-emittingelement material including the carbazole compound can be alight-emitting element having low voltage. Further, the carbazolecompound can also be used for an organic semiconductor material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are conceptual diagrams of light-emitting elements.

FIG. 2 is a conceptual diagram of an organic semiconductor element.

FIGS. 3A and 3B are conceptual diagrams of an active matrixlight-emitting device.

FIGS. 4A and 4B are conceptual diagrams of a passive matrixlight-emitting device.

FIGS. 5A to 5D each illustrate an electronic device.

FIG. 6 illustrates an electronic device.

FIG. 7 illustrates a lighting device.

FIG. 8 illustrates a lighting device.

FIG. 9 illustrates in-vehicle display devices and lighting devices.

FIGS. 10A and 10B are ¹H NMR charts of DBTCzBIm-II.

FIGS. 11A and 11B each show an absorption and emission spectra ofDBTCzBIm-II.

FIGS. 12A and 12B are ¹H NMR charts of DBFCzBIm-II.

FIGS. 13A and 13B each show an absorption and emission spectra ofDBFCzBIm-II.

FIG. 14 shows luminance versus current density characteristics of alight-emitting element 1 and a light-emitting element 2.

FIG. 15 shows luminance versus voltage characteristics of thelight-emitting elements 1 and 2.

FIG. 16 shows current efficiency versus luminance characteristics of thelight-emitting elements 1 and 2.

FIG. 17 shows emission spectra of the light-emitting elements 1 and 2.

FIG. 18 shows changes in normalized luminance versus timecharacteristics of the light-emitting elements 1 and 2.

FIGS. 19A and 19B are CV charts of DBTCzBIm-II in a DMF solution ofDBTCzBIm-II.

FIGS. 20A and 20B are CV charts of DBFCzBIm-II in a DMF solution ofDBFCzBIm-II.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments of the present invention are described. It iseasily understood by those skilled in the art that modes and detailsdisclosed herein can be modified in various ways without departing fromthe spirit and scope of the present invention. Therefore, the presentinvention is not construed as being limited to description of theembodiments.

Embodiment 1

Carbazole compounds in this embodiment each have a structure in whichnitrogen of a carbazole group, the carbazole skeleton of which whose3-position is bonded to the 4-position of a dibenzofuran skeleton or adibenzothiophene skeleton, is bonded to a benzimidazole skeleton througha phenylene group. Note that nitrogen at the 1-position of thebenzimidazole skeleton has an aryl group having 6 to 12 carbon atoms.

The carbazole compound is a novel compound that has a highcarrier-transport property and can be suitably used for a material of alight-emitting element or for an organic semiconductor material.

Note that in the above carbazole compound, carbon in a benzene ring inthe benzimidazole skeleton may have a substituent. The substituent canbe any one of an alkyl group having 1 to 4 carbon atoms, a phenyl group,and a tolyl group. Specific examples of the alkyl group having 1 to 4carbon atoms are a methyl group, an ethyl group, a propyl group, a butylgroup, and the like. When there are two or more carbon atoms havingsubstituents, the substituents may be different from each other.

Further, specific examples of the aryl group having 6 to 12 carbon atomswhich is bonded to nitrogen at the 1-position of the benzimidazoleskeleton are a phenyl group, a naphthyl group, a biphenyl group, and atolyl group.

Carbon in the dibenzofuran skeleton or the dibenzothiophene skeleton mayalso have a substituent. The substituent can be either an alkyl grouphaving 1 to 4 carbon atoms or an aryl group having 6 to 12 carbon atoms.Specific examples of the alkyl group having 1 to 4 carbon atoms are amethyl group, an ethyl group, a propyl group, and a butyl group, andspecific examples of the aryl group having 6 to 12 carbon atoms are aphenyl group, a naphthyl group, a biphenyl group, and a tolyl group.

Further, the carbazole skeleton in the above carbazole compound may havea substituent at the 6-position, and the substituent can be selectedfrom an alkyl group having 1 to 4 carbon atoms and an aryl group having6 to 12 carbon atoms. Specific examples of the alkyl group having 1 to 4carbon atoms are a methyl group, an ethyl group, a propyl group, and abutyl group, and specific examples of the aryl group having 6 to 12carbon atoms are a phenyl group, a naphthyl group, a biphenyl group, anda tolyl group.

The carbazole compound with such a structure has a highcarrier-transport property and can be suitably used for a host materialor a carrier-transport layer in a light-emitting element. Owing to thehigh carrier-transport property of the carbazole compound, alight-emitting element having low driving voltage can be fabricated.

Further, the carbazole compound has a wide band gap, and therefore canbe suitably used for a host material, into which an emission centersubstance that emits blue fluorescence and fluorescence at a longerwavelength than blue or an emission center substance that emits greenphosphorescence and phosphorescence at a longer wavelength than green isdispersed. Since the carbazole compound has a wide band gap and thushigh triplet excitation energy, the energy of carriers that arerecombined in the host material can be effectively transferred to theemission center substance. Accordingly, a light-emitting element withhigh emission efficiency can be fabricated.

Also for a carrier-transport layer adjacent to a light-emitting layercontaining an emission center substance that emits blue fluorescence oran emission center substance that emits green phosphorescence, thecarbazole compound having a wide band gap can be suitably used withoutdeactivating excitation energy of the emission center substance.Accordingly, a light-emitting element with high emission efficiency canbe fabricated.

The above-described carbazole compound can also be represented by thegeneral formula (G1) below.

In the formula, R¹ to R⁴ separately represent any one of hydrogen, analkyl group having 1 to 4 carbon atoms, a phenyl group, and a tolylgroup, and R⁵ represents an aryl group having 6 to 12 carbon atoms. Xrepresents a sulfur atom or an oxygen atom.

Further, R⁶ to R¹³ separately represent any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, and a substituted or unsubstitutedaryl group having 6 to 12 carbon atoms. When the aryl group has asubstituent, an alkyl group having 1 to 4 carbon atoms is a specificexample of the substituent.

In addition, Ph represents a substituted or unsubstituted phenylenegroup; when the phenylene group has a substituent, the substituent canbe an alkyl group having 1 to 4 carbon atoms.

Specific examples of the groups represented by R¹ to R⁴ in the generalformula (G1) are groups represented by the following structural formulae(R-1) to (R-13).

Specific examples of the group represented by R⁵ in the general formula(G1) are groups represented by the following structural formulae (R⁵-1)to (R⁵-11).

Specific examples of the groups represented by R⁶ to R¹³ in the generalformula (G1) are groups represented by the following structural formulae(R-1) to (R-20).

It is preferable in the above general formula (G1) that, when thedibenzothiophene skeleton or the dibenzofuran skeleton has asubstituent, the substituent be positioned at one or more of R⁷, R⁹, andR¹². Such a substituent can be introduced easily through bromination orconversion into boronic acid because of the ease of synthesis. Thestructure in which R⁷ to R¹³ are each hydrogen is further preferablebecause this structure is advantageous in terms of high availability ofa material and can be inexpensively synthesized. For the same reason,also R¹ to R⁴ and R⁶ are preferably each hydrogen.

As Ph, a para-substituted phenyl group is preferred because a highcarrier-transport property can be obtained and an improvement inthermophysical property (for example, a glass-transition temperature:Tg) can also be expected.

Further, a meta-substituted phenylene group is preferred because the usethereof makes the structure of the carbazole compound represented by thegeneral formula (G1) more three-dimensional than that with apara-substituted phenylene group so that an amorphous state can beeasily kept when a film is formed. In addition, a wider band gap and ahigher T1 level than with a para-substituted phenylene group can also beexpected.

Specific examples of structures of the carbazole compound represented bythe above general formula (G1) are substances represented by thefollowing structural formulae (100) to (162) and (200) to (262), and thelike.

The above-described carbazole compounds have an excellentcarrier-transport property and therefore are suitable for acarrier-transport material or a host material; accordingly, alight-emitting element having low driving voltage can also be provided.Further, the carbazole compounds have high triplet excitation energy (alarge energy difference between a triplet excited state and a groundstate), so that a phosphorescent light-emitting element having highemission efficiency can be obtained. In addition, since having hightriplet excitation energy indicates also having a wide band gap, thecarbazole compounds enable even a light-emitting element for emittingblue fluorescence to efficiently emit light. Furthermore, the carbazolecompounds described in this embodiment have a bipolar transportproperty; accordingly, localization of a light-emitting region issuppressed and the influence of triplet-triplet annihilation or the likecan be reduced, which contributes to improvement of emission efficiency.Furthermore, the carbazole compounds in this embodiment have a rigidgroup such as dibenzothiophene or dibenzofuran, and therefore haveexcellent morphology, give stable film quality; and also have anexcellent thermophysical property. In addition, the carbazole compoundscan be used for a light-emitting material that emits blue to ultravioletlight.

Embodiment 2

Next, in this embodiment, a method of synthesizing the carbazolecompound represented by the general formula (G1) below is described. Avariety of reactions can be applied to the method of synthesizing thecarbazole compound. For example, synthesis reactions described belowenable the synthesis of the carbazole compound represented by thegeneral formula (G1).

First, a compound 1 having a halogen group or a triflate group at the3-position of 9H-carbazole is coupled with a boronic acid compound(compound 2) of dibenzofuran (or dibenzothiophene), so that a9H-carbazole derivative having a structure in which the 3-position of9H-carbazole is bonded to the 4-position of dibenzofuran (ordibenzothiophene) (compound 3) can be obtained (reaction formula (A-1)).

In the reaction formula (A-1), X represents oxygen or sulfur, X¹represents a halogen group, a triflate group, or the like, and R⁶ to R¹³separately represent hydrogen, an alkyl group having 1 to 4 carbonatoms, or an aryl group having 6 to 12 carbon atoms. The aryl group mayhave a substituent. Further, the compound 2 may be a boron compound inwhich boronic acid is protected with ethylene glycol or the like. As thecoupling reaction in the reaction formula (A-1), a Suzuki-Miyauracoupling reaction using a palladium catalyst can be used.

Alternatively, for example, a Kumada coupling reaction using a Grignardreagent as substitute for the boronic acid compound in the compound 2, aNegishi coupling reaction using an organozinc compound as substitute forthe boronic acid compound, or a Migita-Kosugi-Stille coupling using anorganotin compound as substitute for the boronic acid compound may beperformed.

Next, the obtained 9H-carbazole derivative (compound 3) is coupled witha halide of a benzimidazole derivative (compound 4), so that a compound(G1) which is the object of the synthesis can be obtained (reactionformula (A-2)).

In the reaction formula (A-2), X represents oxygen or sulfur, X³represents a halogen group or the like, R¹ to R⁴ separately representhydrogen, an alkyl group having 1 to 4 carbon atoms, or a phenyl group,R⁵ represents an aryl group having 6 to 12 carbon atoms, and R⁶ to R¹³separately represent hydrogen, an alkyl group having 1 to 4 carbonatoms, or an aryl group having 6 to 12 carbon atoms. The aryl group mayhave a substituent. The coupling reaction in the reaction formula (A-2)can be performed by a Buchwald-Hartwig reaction using a palladiumcatalyst, an Ullmann reaction using copper or a copper compound, or thelike.

As described above, the carbazole compounds described in Embodiment 1can be synthesized.

Embodiment 3

In this embodiment, an example of the mode in which any of the carbazolecompounds described in Embodiment 1 is used for an active layer of avertical transistor (static induction transistor: SIT), which is a kindof an organic semiconductor element, will be described.

As illustrated in FIG. 2, the element has a structure in which athin-film active layer 1202 containing any of the carbazole compoundsdescribed in Embodiment 1 is interposed between a source electrode 1201and a drain electrode 1203, and a gate electrode 1204 is embedded in theactive layer 1202. The gate electrode 1204 is electrically connected toa means for applying a gate voltage, and the source electrode 1201 andthe drain electrode 1203 are electrically connected to a means forcontrolling a voltage between a source electrode and a drain electrode.

In such an element structure, when a voltage is applied between thesource electrode and the drain electrode without applying a voltage tothe gate electrode, a current flows (on state). Then, by application ofa voltage to the gate electrode in that state, a depletion layer isformed in the periphery of the gate electrode 1204, and the currentceases flowing (off state). With such a mechanism, the element operatesas a transistor.

Like a light-emitting element, a vertical transistor should contain amaterial that realizes both a high carrier-transport property and highquality film for an active layer; the carbazole compounds described inEmbodiment 1 meet such a requirement and therefore can be suitably used.

Embodiment 4

In this embodiment, one mode of a light-emitting element using any ofthe carbazole compounds described in Embodiment 1 is described belowwith reference to FIG. 1A.

A light-emitting element of this embodiment includes a plurality oflayers between a pair of electrodes. In this embodiment, thelight-emitting element includes a first electrode 102, a secondelectrode 104, and a layer 103 containing an organic compound, which isprovided between the first electrode 102 and the second electrode 104.Note that in this embodiment, the first electrode 102 functions as ananode and the second electrode 104 functions as a cathode. In otherwords, when a voltage is applied between the first electrode 102 and thesecond electrode 104 so that the voltage of the first electrode 102 ishigher than that of the second electrode 104, light emission can beobtained.

The substrate 101 is used as a support of the light-emitting element. Asthe substrate 101, glass, plastic or the like can be used, for example.Note that a material other than glass or plastic can be used as far asit can function as a support of the light-emitting element.

For the first electrode 102, any of metals, alloys, electricallyconductive compounds, and mixtures thereof which have a high workfunction (specifically, a work function of 4.0 eV or more) or the likeis preferably used. Specifically, for example, indium oxide-tin oxide(ITO: indium tin oxide), indium oxide-tin oxide containing silicon orsilicon oxide, indium oxide-zinc oxide (IZO: indium zinc oxide), indiumoxide containing tungsten oxide and zinc oxide (IWZO), and the like canbe given. Films of these electrically conductive metal oxides areusually formed by sputtering but may be formed by application of asol-gel method or the like. For example, indium oxide-zinc oxide (IZO)can be formed by a sputtering method using a target in which zinc oxideis added to indium oxide at 1 wt % to 20 wt %. Moreover, indium oxidecontaining tungsten oxide and zinc oxide (IWZO) can be formed by asputtering method using a target in which tungsten oxide is added toindium oxide at 0.5 wt % to 5 wt % and zinc oxide is added to indiumoxide at 0.1 wt % to 1 wt %. Besides, gold (Au), platinum (Pt), nickel(Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron (Fe), cobalt(Co), copper (Cu), palladium (Pd), graphene, nitrides of metal materials(e.g., titanium nitride), and the like can be given.

There is no particular limitation on a stacked structure of the layer103 containing an organic compound. The layer 103 containing an organiccompound can be formed by combining a layer that contains a substancehaving a high electron-transport property, a layer that contains asubstance having a high hole-transport property, a layer that contains asubstance having a high electron-injection property, a layer thatcontains a substance having a high hole-injection property, a layer thatcontains a bipolar substance (a substance having a highelectron-transport and hole-transport property), and the like asappropriate. For example, the layer 103 containing an organic compoundcan be formed by combining a hole-injection layer, a hole-transportlayer, a light-emitting layer, an electron-transport layer, anelectron-injection layer, and the like as appropriate. In thisembodiment, a structure in which the layer 103 containing an organiccompound includes a hole-injection layer 111, a hole-transport layer112, a light-emitting layer 113, and an electron-transport layer 114stacked in this order over the first electrode 102 is described.Materials included in the layers are specifically given below.

The hole-injection layer 111 is a layer containing a substance having ahigh hole-injection property. Molybdenum oxide, vanadium oxide,ruthenium oxide, tungsten oxide, manganese oxide, or the like can beused. Alternatively, the hole-injection layer 111 can be foamed with aphthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc) or copper phthalocyanine (abbreviation: CuPc), an aromatic aminecompound such as4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB) orN,N′-bis[4-[bis(3-methylphenyl)amino]phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: DNTPD), a high molecular compound such aspoly(ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS), orthe like.

Alternatively, a composite material in which a substance having a highhole-transport property contains a substance having an acceptor propertycan be used for the hole-injection layer 111. In this specification, thecomposite material refers to not a material in which two materials aresimply mixed but a material in the state where charge transfer betweenthe materials can be caused by a mixture of a plurality of materials.This charge transfer includes the charge transfer that is realized onlywhen an electric field exists.

Note that the use of such a substance having a high hole-transportproperty which contains a substance having an acceptor property enablesselection of a material used to form an electrode regardless of its workfunction. In other words, besides a material having a high workfunction, a material having a low work function can also be used for thefirst electrode 102. As the substance having an acceptor property,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ), chloranil, and the like can be given. In addition, transitionmetal oxides can be given. Oxides of the metals that belong to Group 4to Group 8 of the periodic table can be given. Specifically, vanadiumoxide, niobium oxide, tantalum oxide, chromium oxide, molybdenum oxide,tungsten oxide, manganese oxide, and rhenium oxide are preferablebecause their electron-accepting property is high. Among these,molybdenum oxide is especially preferable because it is stable in theair and its hygroscopic property is low and is easily treated.

As the substance having a high hole-transport property used for thecomposite material, any of a variety of compounds such as aromatic aminecompounds, carbazole compounds, aromatic hydrocarbons, and highmolecular compounds (e.g., oligomers, dendrimers, or polymers) can beused. Note that the organic compound used for the composite material ispreferably an organic compound having a high hole-transport property.Specifically, a substance having a hole mobility of 10⁻⁶ cm²/Vs or moreis preferably used. Further, other than these substances, any substancethat has a property of transporting more holes than electrons may beused. Organic compounds that can be used as the substance having a highhole-transport property in the composite material are specifically givenbelow.

Examples of the aromatic amine compounds includeN,N′-di(p-tolyl)-N,N′-diphenyl-p-phenylenediamine (abbreviation:DTDPPA), 4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl(abbreviation: DPAB),N,N′-bis[4-[bis(3-methylphenyl)amino]phenyl]-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B), and the like.

Examples of the carbazole compounds that can be used for the compositematerial specifically include3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like.

Examples of the carbazole compounds that can be used for the compositematerial also include 4,4′-di(N-carbazolyl)biphenyl (abbreviation: CBP),1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (abbreviation: TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene, and thelike.

Examples of the aromatic hydrocarbons that can be used for the compositematerial include 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),2-tert-butyl-9,10-bis[2-(1-naphthyl)phenyl]anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene, andthe like. Besides, pentacene, coronene, or the like can also be used.Thus, an aromatic hydrocarbon having 14 to 42 carbon atoms or more andhaving a hole mobility of 1×10⁻⁶ cm²/Vs is more preferably used.

Note that the aromatic hydrocarbons that can be used for the compositematerial may have a vinyl skeleton. Examples of the aromatic hydrocarbonhaving a vinyl group include 4,4′-bis(2,2-diphenylvinyl)biphenyl(abbreviation: DPVBi), 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene(abbreviation: DPVPA), and the like.

Moreover, a high molecular compound such as poly(N-vinylcarbazole)(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](abbreviation: PTPDMA), orpoly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (abbreviation:poly-TPD) can also be used.

The carbazole compounds described in Embodiment 1 are also the aromatichydrocarbon that can be used for the composite material.

The hole-transport layer 112 is a layer that contains a substance havinga high hole-transport property. As the substance having a highhole-transport property, the substances given as the substances having ahigh hole-transport property which can be used for the above compositematerial can also be used. Note that a detailed explanation is omittedto avoid repetition. Refer to the explanation of the composite material.

Since the carbazole compound represented by the general formula (G1)described in Embodiment 1 has a bipolar transport property, thecarbazole compound can be used also for the hole-transport layer 112.Also for a carrier-transport layer adjacent to a light-emitting layercontaining an emission center substance that emits blue fluorescence oran emission center substance that emits green phosphorescence, thecarbazole compound having a wide band gap can be suitably used withoutdeactivating excitation energy of the emission center substance.Accordingly, a light-emitting element with high emission efficiency canbe fabricated. It is needless to say that the carbazole compound can beused for a material included in a carrier-transport layer adjacent to alight-emitting layer containing an emission center substance that emitsfluorescence at a longer wavelength than blue or phosphorescence at alonger wavelength than green or a material included in acarrier-transport layer adjacent to a light-emitting layer containing anemission center substance that emits fluorescence at a shorterwavelength than blue or phosphorescence at a shorter wavelength thangreen.

The light-emitting layer 113 is a layer containing a light-emittingsubstance. The light-emitting layer 113 may be formed with a filmcontaining only a light-emitting substance or a film in which anemission center substance is dispersed into a host material.

There is no particular limitation on a material that can be used as thelight-emitting substance or the emission center substance in thelight-emitting layer 113, and light emitted from the material may beeither fluorescence or phosphorescence. Examples of the abovelight-emitting substance or emission center substance include thefollowing substances: fluorescent substances such asN,N′-bis[4-(9-phenyl-9H-fluoren-9-yl)phenyl]-N,N′-diphenyl-pyrene-1,6-diamine(abbreviation: 1,6-FLPAPrn),N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(abbreviation: 2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene(abbreviation: TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA),N,N″-(2-tert-butylanthracene-9,10-diyldi-4,1-phenylene)bis[N,N′,N′-triphenyl-1,4-phenylenediamine](abbreviation: DPABPA),N,9-diphenyl-N-[4-(9,10-diphenyl-2-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: 2PCAPPA),N-[4-(9,10-diphenyl-2-anthryl)phenyl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPPA),N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetraamine(abbreviation: DBC1), coumarin 30,N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),9,10-bis(1,1′-biphenyl-2-yl)-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA), coumarin 545T, N,N′-diphenylquinacridone(abbreviation: DPQd), rubrene,5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT),2-(2-{2-[4-(dimethylamino)phenyl]ethenyl}-6-methyl-4H-pyran-4-ylidene)propanedinitrile(abbreviation: DCM1),2-{2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCM2),N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD),7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD),2-{2-isopropyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTI),2-{2-tert-butyl-6-[2-(1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: DCJTB),2-(2,6-bis{2-[4-(dimethylamino)phenyl]ethenyl}-4H-pyran-4-ylidene)propanedinitrile(abbreviation: BisDCM), and2-{2,6-bis[2-(8-methoxy-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene}propanedinitrile(abbreviation: BisDCJTM); and phosphorescent substances such asbis[2-(3′,5′-bistrifluoromethylphenyl)pyridinato-N,C^(2′)]iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIracac),tris(2-phenylpyridinato)iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato)iridium(III) acetylacetonate (abbreviation:Ir(ppy)₂(acac)), tris(acetylacetonato)(monophenanthroline)terbium(III)(abbreviation: Tb(acac)₃(Phen)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)),bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III) acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)),bis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′)]iridium(III)(acetylacetonate) (abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphine platinum(II)(abbreviation: PtOEP),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(abbreviation: Eu(DBM)₃(Phen)), andtris[1-(2-thenyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(abbreviation: Eu(TTA)₃(Phen)). Note that the carbazole compoundsaccording to the present invention, typical examples of which includethe carbazole compound represented by the general formula (G1) describedin Embodiment 1, emit light in the blue to ultraviolet region, andtherefore can also be used as an emission center substance.

The carbazole compound represented by the general formula (G1) describedin Embodiment 1 has a wide band gap and has high triplet excitationenergy (a large energy difference between a triplet excited state and aground state), the carbazole compound can be suitably used for a hostmaterial, into which an emission center substance that emits bluefluorescence or an emission center substance that emits greenphosphorescence is dispersed. It is needless to say that the carbazolecompound can be used for a host material, into which an emission centersubstance that emits fluorescence at a longer wavelength than blue orphosphorescence at a longer wavelength than green or an emission centersubstance that emits fluorescence at a shorter wavelength than blue orphosphorescence at a shorter wavelength than green is dispersed. Sincethe carbazole compound has a wide band gap and thus high tripletexcitation energy, the energy of carriers that are recombined in thehost material can be effectively transferred to the emission centersubstance. Accordingly, a light-emitting element with high emissionefficiency can be fabricated. Note that in the case where the carbazolederivative represented by the general formula (G1) described inEmbodiment 1 is used for a host, an emission center substance ispreferably selected from, but not limited to, substances having anarrower band gap or lower triplet excitation energy than the carbazolecompound.

When the carbazole compound represented by the general formula (G1) isnot used as the above host material, any of the following substances canbe used for the host material: metal complex such astris(8-quinolinolato)aluminum(III) (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), andbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ);heterocyclic compounds such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyl)tris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), and9-[4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl]-9H-carbazole (abbreviation:CO11); and aromatic amine compounds such as4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and4,4′-bis[N-(spino-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). In addition, condensed polycyclic aromaticcompounds such as anthracene derivatives, phenanthrene derivatives,pyrene derivatives, chrysene derivatives, and dibenzo[g,p]chrysenederivatives can be given, and specific examples are9,10-diphenylanthracene (abbreviation: DPAnth),N,N-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA),N,9-diphenyl-N-(9,10-diphenyl-2-anthryl)-9H-carbazol-3-amine(abbreviation: 2PCAPA), 6,12-dimethoxy-5,11-diphenylchrysene,N,N,N′,N′,N″,N″,N′″,N′″-octaphenyldibenzo[g,p]chrysene-2,7,10,15-tetramine(abbreviation: DBC1), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyl)anthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diyl)diphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (abbreviation: TPB3), and thelike. Other than these, known materials can be given.

Note that the light-emitting layer 113 can also be a stack of two ormore layers. For example, in the case where the light-emitting layer 113is formed by stacking a first light-emitting layer and a secondlight-emitting layer in that order over the hole-transport layer, forexample, a substance having a hole-transport property is used for thehost material of the first light-emitting layer and a substance havingan electron-transport property is used for the host material of thesecond light-emitting layer.

In the case where the light-emitting layer having the above-describedstructure includes a plurality of materials, co-evaporation by a vacuumevaporation method can be used, or alternatively an inkjet method, aspin coating method, a dip coating method, or the like with a solutionof the materials can be used.

The electron-transport layer 114 is a layer containing a substancehaving a high electron-transport property: for example, a layercontaining a metal complex having a quinoline skeleton or abenzoquinoline skeleton, such as tris(8-quinolinolato)aluminum(abbreviation: Alq), tris(4-methyl-8-quinolinolato)aluminum(abbreviation: Almq₃), bis(10-hydroxybenzo[h]quinolinato)beryllium(abbreviation: BeBq₂), orbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). Alternatively, a metal complex having an oxazole-based orthiazole-based ligand, such as bis[2-(2-hydroxyphenyl)benzoxazolato]zinc(abbreviation: Zn(BOX)₂) or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc(abbreviation: Zn(BTZ)₂), or the like can be used. Besides the metalcomplexes, 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole(abbreviation: PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can also be used. Thesubstances mentioned here mainly have an electron mobility of 10⁻⁶cm²/Vs or more. Note that other than these substances, any substancethat has a property of transporting more electrons than holes may beused.

Since the carbazole derivative represented by the general formula (G1)described in Embodiment 1 has a bipolar transport property, thecarbazole compound can be used also for the electron-transport layer114. Also for a carrier-transport layer adjacent to a light-emittinglayer containing an emission center substance that emits bluefluorescence or an emission center substance that emits greenphosphorescence, the carbazole compound having a wide band gap can besuitably used without deactivating excitation energy of the emissioncenter substance. Accordingly, a light-emitting element with highemission efficiency can be fabricated. It is needless to say that thecarbazole compound can be used for a material included in acarrier-transport layer adjacent to a light-emitting layer containing anemission center substance that emits fluorescence at a longer wavelengththan blue or phosphorescence at a longer wavelength than green or amaterial included in a carrier-transport layer adjacent to alight-emitting layer containing an emission center substance that emitsfluorescence at a shorter wavelength than blue or phosphorescence at ashorter wavelength than green.

Furthermore, the electron-transport layer is not limited to a singlelayer and may be a stack of two or more layers containing any of theabove substances.

Between the electron-transport layer and the light-emitting layer, alayer that controls transport of electron carriers may be provided. Thisis a layer formed by addition of a small amount of a substance having ahigh electron-trapping property to a material having a highelectron-transport property as described above, and capable of adjustingcarrier balance by suppressing transport of electron carriers. Such astructure is very effective in preventing a problem (such as a reductionin element lifetime) caused when electrons pass through thelight-emitting layer.

In addition, an electron-injection layer may be provided in contact withthe second electrode 104 between the electron-transport layer and thesecond electrode 104. For the electron-injection layer, an alkali metal,an alkaline earth metal, or a compound thereof such as lithium fluoride(LiF), cesium fluoride (CsF), or calcium fluoride (CaF₂) can be used.For example, a layer that is formed with a substance having anelectron-transport property and contains an alkali metal, an alkalineearth metal, or a compound thereof, such as an Alq layer containingmagnesium (Mg), can be used. Note that electron injection from thesecond electrode 104 is efficiently performed with the use of a layerthat is formed with a substance having an electron-transport propertyand contains an alkali metal or an alkaline earth metal as theelectron-injection layer, which is preferable.

For the second electrode 104, any of metals, alloys, electricallyconductive compounds, and mixtures thereof which have a low workfunction (specifically, a work function of 3.8 eV or less) or the likecan be used. Specific examples of such a cathode material includeelements that belong to Groups 1 and 2 in the periodic table, i.e.,alkali metals such as lithium (Li) and cesium (Cs), and alkaline earthmetals such as magnesium (Mg), calcium (Ca), and strontium (Sr), alloysthereof (e.g., MgAg or AlLi), rare earth metals such as europium (Eu)and ytterbium (Yb), alloys thereof, and the like. However, when theelectron-injection layer is provided between the second electrode 104and the electron-transport layer, for the second electrode 104, any of avariety of conductive materials such as Al, Ag, ITO, or indium oxide-tinoxide containing silicon or silicon oxide can be used regardless of thework function. Films of these electrically conductive materials can befound by a sputtering method, an inkjet method, a spin coating method,or the like.

Further, any of a variety of methods can be used to form the layer 103containing an organic compound regardless whether it is a dry process ora wet process. For example, a vacuum evaporation method, an inkjetmethod, a spin coating method or the like may be used. Differentformation methods may be used for the electrodes or the layers.

In addition, the electrode may be formed by a wet method using a sol-gelmethod, or by a wet method using paste of a metal material.Alternatively, the electrode may be formed by a dry method such as asputtering method or a vacuum evaporation method.

In the light-emitting element having the above-described structure, acurrent flows due to a potential difference between the first electrode102 and the second electrode 104, and a hole and an electron recombinein the light-emitting layer 113 which contains a substance having a highlight-emitting property, so that light is emitted. That is, alight-emitting region is formed in the light-emitting layer 113.

Light emission is extracted out through one or both of the firstelectrode 102 and the second electrode 104. Therefore, one or both ofthe first electrode 102 and the second electrode 104 arelight-transmitting electrodes. In the case where only the firstelectrode 102 is a light-transmitting electrode, light emission isextracted from the substrate side through the first electrode 102. Inthe case where only the second electrode 104 is a light-transmittingelectrode, light emission is extracted from the side opposite to thesubstrate side through the second electrode 104. In the case where eachof the first electrode 102 and the second electrode 104 is alight-transmitting electrode, light emission is extracted from both thesubstrate side and the side opposite to the substrate through the firstelectrode 102 and the second electrode 104.

The structure of the layers provided between the first electrode 102 andthe second electrode 104 is not limited to the above-describedstructure. Preferably, a light-emitting region where holes and electronsrecombine is positioned away from the first electrode 102 and the secondelectrode 104 so that quenching due to the proximity of thelight-emitting region and a metal used for electrodes andcarrier-injection layers can be prevented. The order of stacking thelayers is not limited to the above structure and may be the followingorder obtained by reversing the order shown in FIG. 1A: the secondelectrode, the electron-injection layer, the electron-transport layer,the light-emitting layer, the hole-transport layer, the hole-injectionlayer, and the first electrode from the substrate side.

Further, in order that transfer of energy from an exciton generated inthe light-emitting layer can be suppressed, preferably, thehole-transport layer and the electron-transport layer which are indirect contact with the light-emitting layer, particularly acarrier-transport layer in contact with a side closer to thelight-emitting region in the light-emitting layer 113 is formed with asubstance having a larger band gap than the light-emitting substance ofthe light-emitting layer or the emission center substance included inthe light-emitting layer.

In the light-emitting element of this embodiment, since any of thecarbazole compounds described in Embodiment 1 having a large band gap isused for the host material and/or for the electron-transport layer,efficient light emission is possible even with the emission centersubstance that has a large band gap and emits blue fluorescence; thus, alight-emitting element with high emission efficiency can be provided.Accordingly, a light-emitting element having lower power consumption canbe provided. In addition, the host material or a material included inthe carrier-transport layer does not easily emit light; accordingly, alight-emitting element capable of light emission with high color puritycan be provided. Further, the carbazole compounds described inEmbodiment 1 have an excellent carrier-transport property; accordingly,a light-emitting element having low driving voltage can be provided.

In this embodiment, the light-emitting element is formed over asubstrate formed of glass, plastic, or the like. With a plurality ofsuch light-emitting elements over one substrate, a passive matrixlight-emitting device can be fabricated. In addition, for example, alight-emitting element may be formed over an electrode electricallyconnected to a thin film transistor (TFT) which is formed over asubstrate formed of glass, plastic, or the like; thus, an active matrixlight-emitting device in which the TFT controls the drive of thelight-emitting element can be fabricated. Note that there is noparticular limitation on the structure of the TFT, which may be astaggered TFT or an inverted staggered TFT. In addition, crystallinityof a semiconductor used for the TFT is not particularly limited either;an amorphous semiconductor or a crystalline semiconductor may be used.In addition, a driver circuit formed in a TFT substrate may be formedwith an n-type TFT and a p-type TFT, or with either an n-type TFT or ap-type TFT.

Embodiment 5

In this embodiment, one mode of a light-emitting element (hereinafter,also referred to as a stacked-type element) having a structure in whicha plurality of light-emitting units is stacked is described withreference to FIG. 1B. This light-emitting element is a light-emittingelement including a plurality of light-emitting units between a firstelectrode and a second electrode. Each light-emitting unit can have thesame structure as the layer 103 containing an organic compound which isdescribed in Embodiment 4. In other words, it can be said that thelight-emitting element described in Embodiment 4 is a light-emittingelement having one light-emitting unit and the light-emitting element inthis embodiment is a light-emitting element having a plurality oflight-emitting units.

In FIG. 1B, a first light-emitting unit 511 and a second light-emittingunit 512 are stacked between a first electrode 501 and a secondelectrode 502, and a charge generation layer 513 is provided between thefirst light-emitting unit 511 and the second light-emitting unit 512.The first electrode 501 and the second electrode 502 correspond,respectively, to the first electrode 102 and the second electrode 104according to Embodiment 4, and materials described in Embodiment 4 canbe used. Further, the structures of the first light-emitting unit 511and the second light-emitting unit 512 may be the same or different.

The charge generation layer 513 contains a composite material of anorganic compound and a metal oxide. This composite material of anorganic compound and a metal oxide is the composite material describedin Embodiment 4, and contains an organic compound and a metal oxide suchas vanadium oxide, molybdenum oxide, or tungsten oxide. As the organiccompound, any of a variety of compounds such as aromatic aminecompounds, carbazole compounds, aromatic hydrocarbons, and highmolecular compounds (oligomers, dendrimers, polymers, or the like) canbe used. Note that as the organic compound, the one having a holemobility of 10⁻⁶ cm²/Vs or more as an organic compound having ahole-transport property is preferably used. Further, other than thesesubstances, any substance that has a property of transporting more holesthan electrons may be used. Since a composite of an organic compound anda metal oxide is excellent in carrier-injection property andcarrier-transport property, low voltage driving and low current drivingcan be realized.

The charge generation layer 513 may be formed in such a way that a layercontaining the composite material of an organic compound and a metaloxide is combined with a layer containing another material, for example,with a layer that contains a compound selected from substances having anelectron-donating property and a compound having a highelectron-transport property. The charge generation layer 513 may beformed in such a way that a layer containing the composite material ofan organic compound and a metal oxide is combined with a transparentconductive film.

The charge generation layer 513 interposed between the firstlight-emitting unit 511 and the second light-emitting unit 512 may haveany structure as far as electrons can be injected to a light-emittingunit on one side and holes can be injected to a light-emitting unit onthe other side when a voltage is applied between the first electrode 501and the second electrode 502. For example, in FIG. 1B, any layer can beused as the charge generation layer 513 as far as the layer injectselectrons into the first light-emitting unit 511 and holes into thesecond light-emitting unit 512 when a voltage is applied such that thevoltage of the first electrode is higher than that of the secondelectrode.

Although the light-emitting element having two light-emitting units isdescribed in this embodiment, the present invention can be similarlyapplied to a light-emitting element in which three or morelight-emitting units are stacked. By arrangement of a plurality oflight-emitting units, which are partitioned by the charge-generationlayer between a pair of electrodes, as in the light-emitting element ofthis embodiment, light emission in a high luminance region can berealized with current density kept low, thus light-emitting having along lifetime can be realized. Further, in application to lightingdevices, since a voltage drop due to resistance of an electrode materialcan be reduced, light emission in a large area is possible. Moreover, alight-emitting device having low driving voltage and having lower powerconsumption can be realized.

By making emission colors of the light-emitting units different fromeach other, light emission with a desired color can be obtained from thelight-emitting element as a whole. For example, in a light-emittingelement including two light-emitting units, the emission colors of thefirst light-emitting unit and the second light-emitting unit are madecomplementary, so that the light-emitting element which emits whitelight as the whole element can be obtained. Note that the term“complementary” means color relationship in which an achromatic color isobtained when colors are mixed. That is, a mixture of light emissionswith complementary colors gives white light emission. The same can beapplied to a light-emitting element including three light-emittingunits. For example, the light-emitting element as a whole can emit whitelight when the emission color of the first light-emitting unit is red,the emission color of the second light-emitting unit is green, and theemission color of the third light-emitting unit is blue.

Since the light-emitting element of this embodiment includes any of thecarbazole compounds described in Embodiment 1, the light-emittingelement can be a light-emitting element that has high emissionefficiency and low driving voltage. In addition, since light emissionwith high color purity which originates from the emission centersubstance can be obtained from the light-emitting unit including thecarbazole compound, color adjustment of the light-emitting element as awhole is easy.

Note that this embodiment can be combined with any of the otherembodiments as appropriate.

Embodiment 6

In this embodiment, a light-emitting device including a light-emittingelement including any of the carbazole compounds described in Embodiment1 is described.

In this embodiment, an example of the light-emitting device fabricatedusing a light-emitting element including any of the carbazole compoundsdescribed in Embodiment 1 is described with reference to FIGS. 3A and3B. Note that FIG. 3A is a top view illustrating the light-emittingdevice and FIG. 3B is a cross-sectional view of FIG. 3A taken alonglines A-A′ and B-B′. This light-emitting device includes a drivercircuit portion (source driver circuit) 601, a pixel portion 602, and adriver circuit portion (gate driver circuit) 603, which are to controllight emission of the light-emitting element and illustrated with dottedlines. Moreover, a reference numeral 604 denotes a sealing substrate;605, a sealing material; and 607, a space surrounded by the sealingmaterial 605.

Reference numeral 608 denotes a wiring for transmitting signals to beinputted into the source driver circuit 601 and the gate driver circuit603 and receiving signals such as a video signal, a clock signal, astart signal, and a reset signal from an FPC (flexible printed circuit)609 serving as an external input terminal. Although only the FPC isillustrated here, a printed wiring board (PWB) may be attached to theFPC. The light-emitting device in the present specification includes, inits category, not only the light-emitting device itself but also thelight-emitting device provided with the FPC or the PWB.

Next, a cross-sectional structure is described with reference to FIG.3B. The driver circuit portion and the pixel portion are formed over anelement substrate 610; the source driver circuit 601, which is a drivercircuit portion, and one of the pixels in the pixel portion 602 areillustrated here

As the source driver circuit 601, a CMOS circuit in which an n-channelTFT 623 and a p-channel TFT 624 are combined is formed. In addition, thedriver circuit may be formed with any of a variety of circuits such as aCMOS circuit, a PMOS circuit, or an NMOS circuit. Although a driverintegrated type in which the driver circuit is formed over the substrateis illustrated in this embodiment, the driver circuit may notnecessarily be formed over the substrate, and the driver circuit can beformed outside, not over the substrate.

The pixel portion 602 includes a plurality of pixels including aswitching TFT 611, a current controlling TFT 612, and a first electrode613 electrically connected to a drain of the current controlling TFT.Note that to cover an end portion of the first electrode 613, aninsulator 614 is formed, for which a positive type photosensitiveacrylic resin film is used here.

In order to improve coverage, the insulator 614 is formed to have acurved surface with curvature at its upper or lower end portion. Forexample, in the case where positive photosensitive acrylic is used for amaterial of the insulator 614, only the upper end portion of theinsulator 614 preferably has a curved surface with a curvature radius(0.2 μm to 3 μm). As the insulator 614, either a negative type thatbecomes insoluble in an etchant by irradiation with light or a positivetype that becomes soluble in an etchant by irradiation with light can beused.

A layer 616 containing an organic compound and a second electrode 617are formed over the first electrode 613. Here, as a material used forthe first electrode 613 functioning as an anode, a material having ahigh work function is preferably used. For example, a single-layer filmof an ITO film, an indium tin oxide film containing silicon, an indiumoxide film containing zinc oxide at 2 wt % to 20 wt %, a titaniumnitride film, a chromium film, a tungsten film, a Zn film, a Pt film, orthe like, a stack of a titanium nitride film and a film containingaluminum as its main component, a stack of three layers of a titaniumnitride film, a film containing aluminum as its main component, and atitanium nitride film, or the like can be used. Note that when thestacked structure is used, the first electrode 613 has low resistance asa wiring, forms a favorable ohmic contact, and can function as an anode.

In addition, the layer 616 containing an organic compound is formed byany of a variety of methods such as an evaporation method using a shadowmask, an inkjet method, and a spin coating method. The layer 616containing an organic compound contains any of the carbazole compoundsdescribed in Embodiment 1. Further, another material included in thelayer 616 containing an organic compound may be a low molecular compoundor a high molecular compound (which may be an oligomer and a dendrimer).

As a material used for the second electrode 617, which is formed overthe layer 616 containing an organic compound and functions as a cathode,a material having a low work function (e.g., Al, Mg, Li, Ca, or an alloyor compound thereof, such as MgAg, MgIn, or AlLi) is preferably used. Inthe case where light generated in the layer 616 containing an organiccompound passes through the second electrode 617, a stack of a thinmetal film and a transparent conductive film (e.g., ITO, indium oxidecontaining zinc oxide at 2 wt % to 20 wt %, indium tin oxide containingsilicon, or zinc oxide (ZnO)) is preferably used for the secondelectrode 617.

Note that the light-emitting element is formed with the first electrode613, the layer 616 containing an organic compound, and the secondelectrode 617. The light-emitting element has any of the structuresdescribed in Embodiments 4 and 5. In the light-emitting device of thisembodiment, the pixel portion, which includes a plurality oflight-emitting elements, may include both the light-emitting elementwith any of the structures described in Embodiments 4 and 5 and alight-emitting element with a structure other than those.

Further, the sealing substrate 604 is attached to the element substrate610 with the sealing material 605, so that a light-emitting element 618is provided in the space 607 surrounded by the element substrate 610,the sealing substrate 604, and the sealing material 605. The space 607may be filled with filler, and may be filled with an inert gas (such asnitrogen or argon), or the sealing material 605.

Note that an epoxy based resin is preferably used for the sealingmaterial 605. It is desirable that such a material do not transmitmoisture or oxygen as much as possible. As a material for the sealingsubstrate 604, a plastic substrate formed of FRP (fiberglass-reinforcedplastics), PVF (polyvinyl fluoride), polyester, acrylic, or the like canbe used besides a glass substrate or a quartz substrate.

As described above, the light-emitting device fabricated using thelight-emitting element containing any of the carbazole compoundsdescribed in Embodiment 1 can be obtained.

The light-emitting element containing any of the carbazole compoundsdescribed in Embodiment 1 is used in the light-emitting device in thisembodiment, and thus a light-emitting device having favorablecharacteristics can be obtained. Specifically, the carbazole compoundsdescribed in Embodiment 1 have a large band gap and high tripletexcitation energy and can suppress energy transfer from a light-emittingsubstance; accordingly, a light-emitting element having high emissionefficiency can be provided, so that a light-emitting device havingreduced power consumption can be provided. In addition, a light-emittingelement having low driving voltage can be provided, so that alight-emitting device having low driving voltage can be provided.

Although an active matrix light-emitting device is thus described above,a passive matrix light-emitting device is described below. FIGS. 4A and4B illustrate a passive matrix light-emitting device fabricatedaccording to the present invention. FIG. 4A is a perspective view of thelight-emitting device, and FIG. 4B is a cross-sectional view taken alongline X-Y in FIG. 4A. In FIGS. 4A and 4B, over a substrate 951, a layer955 containing an organic compound is provided between an electrode 952and an electrode 956. An end portion of the electrode 952 is coveredwith an insulating layer 953. In addition, a partition layer 954 isprovided over the insulating layer 953. The sidewalls of the partitionlayer 954 are aslope such that the distance between both sidewalls isgradually narrowed toward the surface of the substrate. In other words,a cross section taken along the direction of the short side of thepartition wall layer 954 is trapezoidal, and the lower side (a sidewhich is in the same direction as a plane direction of the insulatinglayer 953 and in contact with the insulating layer 953) is shorter thanthe upper side (a side which is in the same direction as the planedirection of the insulating layer 953 and not in contact with theinsulating layer 953). The partition layer 954 thus provided can preventa defect in the light-emitting element due to static charge or the like.The passive matrix light-emitting device can also be driven with lowpower consumption by including the light-emitting element according toEmbodiment 4 or 5 which contains any of the carbazole compoundsdescribed in Embodiment 1 and is capable of operating at low voltage. Inaddition, the light-emitting device can be driven with low powerconsumption by including the light-emitting element according toEmbodiment 4 or 5 which contains any of the carbazole compoundsdescribed in Embodiment 1 and therefore has high emission efficiency.

Since many minute light-emitting elements arranged in a matrix in thelight-emitting device described above can each be controlled, thelight-emitting device can be suitably used as a display device fordisplaying images.

Embodiment 7

In this embodiment, electronic devices each including the light-emittingelement described in Embodiment 4 or 5 are described. The light-emittingelement described in Embodiment 4 or 5 has reduced power consumptionsince it includes any of the carbazole compounds described in Embodiment1; accordingly, the electronic devices described in this embodiment canbe electronic devices each including a display portion having reducedpower consumption. In addition, they can be electronic devices havinglow driving voltage since the light-emitting element described inEmbodiment 4 or 5 is a light-emitting element having low drivingvoltage.

Examples of the electronic devices to which the above light-emittingelement is applied are television devices (also referred to as TV ortelevision receivers), monitors for computers and the like, cameras suchas digital cameras and digital video cameras, digital photo frames,cellular phones (also referred to as portable telephone devices),portable game machines, portable information terminals, audio playbackdevices, large game machines such as pin-ball machines, and the like.Specific examples of these electronic devices are described below.

FIG. 5A illustrates an example of a television device. In the televisiondevice, a display portion 7103 is incorporated in a housing 7101. Inaddition, here, the housing 7101 is supported by a stand 7105. Thedisplay portion 7103 enables display of images and includeslight-emitting elements which are the same as that described inEmbodiment 4 or 5 and arranged in a matrix. Since each light-emittingelement includes any of the carbazole compounds described in Embodiment1, the light-emitting elements can be light-emitting elements havinghigh emission efficiency, or can be light-emitting elements having lowdriving voltage. Accordingly, the television device that has the displayportion 7103 including the light-emitting elements can be a televisiondevice having reduced power consumption or can be a television devicehaving low driving voltage.

The television device can be operated by an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthermore, the remote controller 7110 may be provided witha display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television device is provided with a receiver, a modem,and the like. With the receiver, general television broadcasting can bereceived. Furthermore, when the television device is connected to acommunication network by wired or wireless connection via the modem,one-way (from a transmitter to a receiver) or two-way (between atransmitter and a receiver, between receivers, or the like) datacommunication can be performed.

FIG. 5B illustrates a computer having a main body 7201, a housing 7202,a display portion 7203, a keyboard 7204, an external connecting port7205, a pointing device 7206, and the like. Note that this computer ismanufactured by using light-emitting elements arranged in a matrix inthe display portion 7203, which are the same as that described inEmbodiment 4 or 5. Since each light-emitting element includes any of thecarbazole compounds described in Embodiment 1, the light-emittingelements can be light-emitting elements having high emission efficiency,or can be light-emitting elements having low driving voltage.Accordingly, the computer that has the display portion 7203 includingthe light-emitting elements can be a computer having reduced powerconsumption or can be a computer having low driving voltage.

FIG. 5C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be opened or folded.A display portion 7304 including light-emitting elements which are thesame as that described in Embodiment 4 or 5 and arranged in a matrix isincorporated in the housing 7301, and a display portion 7305 isincorporated in the housing 7302. In addition, the portable game machineillustrated in FIG. 5C includes a speaker portion 7306, a recordingmedium insertion portion 7307, an LED lamp 7308, an input unit (anoperation key 7309, a connection terminal 7310, a sensor 7311 (a sensorhaving a function of measuring force, displacement, position, speed,acceleration, angular velocity, rotational frequency, distance, light,liquid, magnetism, temperature, chemical substance, sound, time,hardness, electric field, current, voltage, electric power, radiation,flow rate, humidity, gradient, oscillation, odor, or infrared rays), ora microphone 7312), and the like. It is needless to say that thestructure of the portable games machine is not limited to the above asfar as the display portion including light-emitting elements which arethe same as that described in Embodiment 4 or 5 and arranged in a matrixis used as at least either the display portion 7304 or the displayportion 7305, or both, and the structure can include other accessoriesas appropriate. The portable game machine illustrated in FIG. 5C has afunction of reading out a program or data stored in a storage medium todisplay it on the display portion, and a function of sharing informationwith another portable game machine by wireless communication. Theportable game machine illustrated in FIG. 5C can have a variety offunctions without limitation to the above. The portable game machineincluding the above-described display portion 7304 can be a portablegame machine having reduced power consumption because the light-emittingelements used in the display portion 7304 have high emission efficiencyby including any of the carbazole compounds described in Embodiment 1.The portable game machine can also be a portable game machine having lowdriving voltage because the light-emitting elements used in the displayportion 7304 has low driving voltage by including any of the carbazolecompounds described in Embodiment 1.

FIG. 5D illustrates an example of a cellular phone. The cellular phone7400 is provided with operation buttons 7403, an external connectionport 7404, a speaker 7405, a microphone 7406, and the like, in additionto a display portion 7402 incorporated in a housing 7401. Note that thecellular phone 7400 has the display portion 7402 includinglight-emitting elements which are the same as that described inEmbodiment 4 or 5 and arranged in a matrix. Since each light-emittingelement includes any of the carbazole compounds described in Embodiment1, the light-emitting elements can be light-emitting elements havinghigh emission efficiency, or can be light-emitting elements having lowdriving voltage. Accordingly, the cellular phone that has the displayportion 7402 including the light-emitting elements can be a cellularphone having reduced power consumption or can be a cellular phone havinglow driving voltage.

When the display portion 7402 of the cellular phone illustrated in FIG.5D is touched with a finger or the like, data can be input into thecellular phone. In this case, operations such as making a call andcreating e-mail can be performed by touch on the display portion 7402with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying an image. The secondmode is an input mode mainly for inputting information such ascharacters. The third mode is a display-and-input mode in which twomodes of the display mode and the input mode are mixed.

For example, in the case of making a call or creating e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on a screen can be input. In this case, itis preferable to display a keyboard or number buttons on almost theentire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside thecellular phone, display on the screen of the display portion 7402 can beautomatically changed by determining the orientation of the cellularphone (whether the cellular phone is placed horizontally or verticallyfor a landscape mode or a portrait mode).

The screen modes are switched by touch on the display portion 7402 oroperation with the operation buttons 7403 of the housing 7401.Alternatively, the screen modes can be switched depending on the kindsof images displayed on the display portion 7402. For example, when asignal for an image displayed on the display portion is data of movingimages, the screen mode is switched to the display mode. When the signalis text data, the screen mode is switched to the input mode.

Moreover, in the input mode, if a signal detected by an optical sensorin the display portion 7402 is detected and the input by touch on thedisplay portion 7402 is not performed during a certain period, thescreen mode may be controlled so as to be switched from the input modeto the display mode.

The display portion 7402 can function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken by touchon the display portion 7402 with the palm or the finger, so thatpersonal authentication can be performed. Furthermore, by use of abacklight or a sensing light source that emits a near-infrared light forthe display portion, an image of a finger vein, a palm vein, or the likecan also be taken.

Note that the structure described in this embodiment can be combinedwith any of the structures described in Embodiments 1 to 3 asappropriate.

As described above, the application range of the light-emitting devicehaving the light-emitting element according to Embodiment 4 or 5 whichincludes any of the carbazole compounds described in Embodiment 1 iswide so that this light-emitting device can be applied to electronicdevices in a variety of fields. By use of any of the carbazole compoundsdescribed in Embodiment 1, an electronic device having reduced powerconsumption or an electronic device having low driving voltage can beobtained.

The light-emitting element described in Embodiment 4 or 5 can also beused for a lighting device. One mode of application of thelight-emitting element described in Embodiment 4 or 5 to a lightingdevice is described with reference to FIG. 6. Note that the lightingdevice includes the light-emitting element described in Embodiment 4 or5 as a light irradiation unit and at least includes an input-outputterminal portion that supplies a current to the light-emitting element.Further, the light-emitting element is preferably shielded from theoutside atmosphere by sealing.

FIG. 6 illustrates an example of a liquid crystal display device usingthe light-emitting element described in Embodiment 4 or 5 for abacklight. The liquid crystal display device illustrated in FIG. 6includes a housing 901, a liquid crystal layer 902, a backlight 903, anda housing 904. The liquid crystal layer 902 is connected to a driver IC905. The light-emitting element described in Embodiment 4 or 5 is usedin the backlight 903, to which a current is supplied through a terminal906.

The light-emitting element described in Embodiment 4 or 5 is used forthe backlight of the liquid crystal display device, and thus a backlighthaving reduced power consumption can be obtained. In addition, use ofthe light-emitting element described in Embodiment 4 or 5 enablesmanufacture of a planar-emission lighting device and further alarger-area planar-emission lighting device; therefore, the backlightcan be a larger-area backlight, and the liquid crystal display devicecan also be a larger-area device. Furthermore, the backlight using thelight-emitting element described in Embodiment 4 or 5 can be thinnerthan a conventional one; accordingly, the display device can also bethinner.

FIG. 7 illustrates an example in which the light-emitting elementdescribed in Embodiment 4 or 5 is used for a table lamp which is alighting device. The table lamp illustrated in FIG. 7 includes a housing2001 and a light source 2002, and the light-emitting element describedin Embodiment 4 or 5 is used for the light source 2002.

FIG. 8 illustrates an example in which the light-emitting elementdescribed in Embodiment 4 or 5 is used for indoor lighting devices 3001and 3002. Since the light-emitting element described in Embodiment 4 or5 has reduced power consumption, a lighting device that has reducedpower consumption can be obtained. Further, since the light-emittingelement described in Embodiment 4 or 5 can have a large area, thelight-emitting element can be used for a large-area lighting device.Furthermore, since the light-emitting element described in Embodiment 4or 5 is thin, a lighting device having a reduced thickness can befabricated.

The light-emitting element described in Embodiment 4 or 5 can also beused for an automobile windshield or dashboard. One mode in which thelight-emitting elements described in Embodiment 4 or 5 are used for anautomobile windshield and an automobile dashboard is illustrated in FIG.9. Displays 5000 to 5005 each include the light-emitting elementdescribed in Embodiment 4 or 5.

The display 5000 and the display 5001 are display devices which areprovided in the automobile windshield and in which the light-emittingelements described in Embodiment 4 or 5 are incorporated. Thelight-emitting elements described in Embodiment 4 or 5 can be formedinto so-called see-through display devices, through which the oppositeside can be seen, by including a first electrode and a second electrodeformed with electrodes having a light-transmitting property. Suchsee-through display devices can be provided even in the automobilewindshield, without hindering the vision. Note in the case where atransistor for driving the light-emitting element is provided, atransistor having a light-transmitting property, such as an organictransistor using an organic semiconductor material or a transistor usingan oxide semiconductor, is preferably used.

The display 5002 is a display device which is provided in a pillarportion and in which the light-emitting element described in Embodiment4 or 5 is incorporated. The display 5002 can compensate for the viewhindered by the pillar portion by showing an image taken by an imagingelement provided in the automobile body. Similarly, the display 5003provided in the dashboard can compensate for the view hindered by theautomobile body by showing an image taken by an imaging element providedin the outside of the automobile body, which leads to elimination ofblind areas and enhancement of safety. Showing an image so as tocompensate for the area which a driver cannot see, makes it possible forthe driver to confirm safety easily and comfortably.

The display 5004 and the display 5005 can provide a variety of kinds ofinformation such as information of navigation, speedometer, tachometer,mileage (travel distance), fuel meter, gearshift indicator, and aircondition. The content or layout of the display can be changed freely bya user as appropriate. Further, such information can also be shown inthe displays 5000 to 5003. Note that the displays 5000 to 5005 can alsobe used as lighting devices.

By including any of the carbazole compounds described in Embodiment 1,the light-emitting element described in Embodiment 4 or 5 has lowdriving voltage and lower power consumption. When a number of largescreens are provided, load on a battery can be reduced, which providescomfortable use. The light-emitting device and the lighting device eachusing the light-emitting element described in Embodiment 4 or 5 can besuitably used as an in-vehicle light-emitting device or lighting device.

Example 1 Synthesis Example 1

In this example, a method of synthesizing2-[4-{3-(dibenzothiophen-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBTCzBIm-II), which is the carbazole derivativerepresented by the general formula (G1), is described. A structure ofDBTCzBIm-II is illustrated in the following structural formula (100).

First, a method of synthesizing 3-(dibenzothiophen-4-yl)-9H-carbazole,which is a synthetic intermediate of DBTCzBIm-II, will be described.3-(Dibenzothiophen-4-yl)-9H-carbazole is a carbazole derivativerepresented by the following structural formula.

Step 1: Synthesis of 3-(Dibenzothiophen-4-yl)-9H-carbazole

Into a 200 mL three-neck flask were placed 3.0 g (12 mmol) of3-bromocarbazole, 2.8 g (12 mmol) of dibenzothiophene-4-boronic acid,and 150 mg (0.5 mol) of tri(ortho-tolyl)phosphine, and the air in theflask was replaced with nitrogen. To this mixture were added 40 mL oftoluene, 40 mL of ethanol, and 15 mL (2.0 mol/L) of an aqueous solutionof potassium carbonate. In the flask, the mixture was degassed by beingstirred under reduced pressure. After the degassing, replacement withnitrogen was performed, and 23 mg (0.10 mmol) of palladium(II) acetatewas added to this mixture, and then the mixture was refluxed at 110° C.for 3 hours. After the reflux, the mixture was cooled to roomtemperature, and then the obtained solid was collected by suctionfiltration. The collected solid was dissolved in 100 mL of toluene, andthis solution was filtered through Celite (produced by Wako PureChemical Industries, Ltd., Catalog No. 531-16855), Florisil (produced byWako Pure Chemical Industries, Ltd., Catalog No. 540-00135), andalumina. The solid obtained by concentration of the obtained filtratewas recrystallized from toluene/hexane, so that 1.4 g of a white solidwas obtained in 32% yield. The synthesis scheme of Step 1 is illustratedin the formula (a-1).

Step 2: Synthesis ofN-Phenyl-2-{4-[3-(dibenzothiophen-4-yl)-9H-carbazol-9-yl]phenyl}benzimidazole(abbreviation: DBTCzBIm-II)

Into a 100 mL three-neck flask were placed 0.36 g (1.0 mmol) ofN-phenyl-2-(4-bromophenyl)benzimidazole and 0.36 g (1.0 mmol) of3-(dibenzothiophen-4-yl)-9H-carbazole, and the air in the flask wasreplaced with nitrogen. To this mixture were added 10 mL of toluene,0.10 mL of tri(tert-butyl)phosphine (a 10 wt % hexane solution), and0.15 g (4.3 mmol) of sodium tert-butoxide. This mixture was degassedwhile being stirred under reduced pressure. After this mixture washeated to 80° C., 5.0 mg (0.025 mmol) ofbis(dibenzylideneacetone)palladium(0) was added thereto, and then themixture was stirred at 80° C. for 3 hours. After the stirring, 14 mg(0.025 mmol) of bis(dibenzylideneacetone)palladium(0) was added to thismixture, and then it was further stirred at 110° C. for 7.5 hours. Afterthe stirring, about 30 mL of toluene was added to the mixture, and thenit was stirred at 80° C. This mixture was subjected to hot filtrationwith ethyl acetate through Celite (produced by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855), Florisil (produced by WakoPure Chemical Industries, Ltd., Catalog No. 540-00135), and alumina. Theobtained filtrate was concentrated to give a white solid. The obtainedsolid was dissolved in toluene. The mixture was purified by silica gelcolumn chromatography (a developing solvent in which the ratio of hexaneto ethyl acetate was 4:1), and further recrystallized fromtoluene/hexane, so that 0.41 g of a white solid was obtained in 65%yield. The synthesis scheme of Step 2 is illustrated in the formula(b-1).

Then, 0.40 g of the obtained white solid was purified by sublimation. Atrain sublimation method was used, and the obtained white solid washeated at 290° C. under a pressure of 2.3 Pa with a flow rate of argongas of 5.0 of mL/min. After purification by sublimation, 0.32 g of acolorless transparent solid was recovered in 78% yield.

The colorless transparent solid after purification by sublimation wassubjected to nuclear magnetic resonance (¹H NMR) spectroscopy. Themeasurement data are shown below. In addition, ¹H NMR charts are shownin FIGS. 10A and 10B. Note that FIG. 10B is a chart where the range offrom 7.00 ppm to 8.75 ppm in FIG. 10A is enlarged.

¹H NMR (CDCl₃, 300 MHz): δ=7.31-7.42 (m, 4H), 7.44-7.49 (m, 6H),7.51-7.64 (m, 8H), 7.79-7.89 (m, 4H), 7.94 (d, J=7.8 Hz, 1H), 8.45-8.23(m, 3H), 8.49 (d, J=2.1 Hz, 1H)

The measurement results showed that DBTCzBIm-II, which is the carbazolederivative represented by the above structural formula (100), wasobtained.

Further, an absorption and emission spectra of DBTCzBIm-II in a toluenesolution of DBTCzBIm-II are shown in FIG. 11A, and an absorption andemission spectra of a thin film of DBTCzBIm-II are shown in FIG. 11B. Anultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation) was used for the measurements of the spectra. The spectraof the toluene solution were measured with a toluene solution ofDBTCzBIm-II put in a quartz cell. The spectra of the thin film weremeasured with a sample prepared by evaporation of DBTCzBIm-II on aquartz substrate. Note that in the case of the absorption spectrum ofthe toluene solution, the absorption spectrum obtained by subtraction ofthe absorption spectra of quartz and toluene from the measured spectrais shown in the drawing, and in the case of the absorption spectrum ofthe thin film, the absorption spectrum obtained by subtraction of thatof the quartz substrate from the measured spectra is shown in thedrawing.

FIG. 11A shows that the greatest emission wavelength of DBTCzBIm-II inthe toluene solution of DBTCzBIm-II is around 377 nm (at an excitationwavelength of 340 nm), and FIG. 11B shows that the greatest emissionwavelength of the thin film of DBTCzBIm-II is around 402 nm (at anexcitation wavelength of 339 nm).

Further, the ionization potential of DBTCzBIm-II in a thin film statewas measured by a photoelectron spectrometer (AC-2, produced by RikenKeiki, Co., Ltd.) in the air. The obtained value of the ionizationpotential was converted to a negative value, so that the HOMO level ofDBTCzBIm-II was −5.68 eV. From the data of the absorption spectra of thethin film in FIG. 11B, the absorption edge of DBTCzBIm-II, which wasobtained from a Tauc plot with an assumption of direct transition, was3.31 eV. Therefore, the optical band gap of DBTCzBIm-II in the solidstate was estimated at 3.31 eV; from the values of the HOMO levelobtained above and this band gap, the LUMO level of DBTCzBIm-II was ableto be estimated at −2.37 eV. It was thus found that DBTCzBIm-II had awide band gap of 3.31 eV in the solid state.

Further, the oxidation and reduction characteristics of DBTCzBIm-II weremeasured. These were examined by cyclic voltammetry (CV) measurement.Note that an electrochemical analyzer (ALS model 600A or 600C, producedby BAS Inc.) was used for the measurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, produced by Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,produced by Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, producedby BAS Inc.) was used as a working electrode; a platinum electrode (aVC-3 Pt counter electrode (5 cm), produced by BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, produced by BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements of the oxidation characteristics, scanning in whichthe potential of the working electrode with respect to the referenceelectrode was changed from 0.00 V to 1.10 V and then changed from 1.10 Vto 0.00 V was one cycle, and 100-cycle measurements were performed. Inthe measurements of the reduction characteristics, scanning in which thepotential of the working electrode with respect to the referenceelectrode was changed from −1.57 V to −2.67 V and then changed from−2.67 V to −1.57 V was one cycle, and 100-cycle measurements wereperformed. The measurement results are shown in FIGS. 19A and 19B. Notethat FIG. 19A shows a CV chart of the oxidation characteristics, andFIG. 19B shows a CV chart of the reduction characteristics.

The measurement results revealed that DBTCzBIm-II showed a propertyeffective against repetition of redox reactions between an oxidizedstate and a neutral state and repetition of redox reactions between areduced state and a neutral state, without large variations in theoxidation and reduction peaks of the oxidation and reductioncharacteristics even after the 100-cycle measurements.

Further, the HOMO and LUMO levels of DBTCzBIm-II were calculated alsofrom the CV measurement results.

First, the potential energy of the reference electrode (Ag/Ag⁺electrode) with respect to the vacuum level, which was used, is −4.94eV.

According to FIG. 19A showing the oxidation characteristics, theoxidation peak potential E_(pa) of DBTCzBIm-II was 1.03 V. In addition,the reduction peak potential E_(pc) thereof was 0.90 V. Therefore, thehalf-wave potential (intermediate potential between E_(pa) and E_(pc))can be calculated at 0.97 V. This means that DBTCzBIm-II is oxidized byan electric energy of 0.97 [V vs. Ag/Ag⁺], and this energy correspondsto the HOMO level. Here, since the potential energy of the referenceelectrode, which was used in this example, with respect to the vacuumlevel is −4.94 [eV] as described above, the HOMO level of DBTCzBIm-IIwas found to be as follows: −4.94−0.97=−5.91 [eV].

Similarly, according to FIG. 19B showing the reduction characteristics,the oxidation peak potential E_(pa) of DBFCzBIm-II was −2.47 V, and thereduction peak potential E_(pc) thereof was −2.61V. Therefore, thehalf-wave potential (intermediate potential between E_(pa) and E_(pc))can be calculated at −2.54 V. This means that DBFCzBIm-II is reduced byan electric energy of −2.54 [V vs. Ag/Ag⁺], and this energy correspondsto the LUMO level. Here, since the potential energy of the referenceelectrode, which was used in this example, with respect to the vacuumlevel is −4.94 [eV] as described above, the LUMO level of DBFCzBIm-IIwas found to be as follows: −4.94−(−2.54)=−2.40 [eV].

Note that the potential energy of the reference electrode (Ag/Ag⁺electrode) with respect to the vacuum level corresponds to the Fermilevel of the Ag/Ag⁺ electrode, and should be calculated from a valueobtained by measuring a substance whose potential energy with respect tothe vacuum level is known, with the use of the reference electrode(Ag/Ag⁺ electrode).

How the potential energy (eV) of the reference electrode (Ag/Ag⁺electrode), which was used in this example, with respect to the vacuumlevel is calculated will be specifically described. It is known that theoxidation-reduction potential of ferrocene in methanol is +0.610 V [vs.SHE] with respect to the standard hydrogen electrode (reference:Christian R. Goldsmith et al., J. Am. Chem. Soc., Vol. 124, No. 1, pp.83-96, 2002). In contrast, using the reference electrode used in thisexample, the oxidation-reduction potential of ferrocene in methanol wascalculated at +0.11V [vs. Ag/Ag⁺]. Thus, it was found that the potentialenergy of this reference electrode was lower than that of the standardhydrogen electrode by 0.50 [eV].

Here, it is known that the potential energy of the standard hydrogenelectrode with respect to the vacuum level is −4.44 eV (reference:Toshihiro Ohnishi and Tamami Koyama, High molecular EL material,Kyoritsu shuppan, pp. 64-67). Therefore, the potential energy of thereference electrode used in this example with respect to the vacuumlevel can be calculated as follows: −4.44−0.50=−4.94 [eV].

Example 2 Synthesis Example 2

In this example, a method of synthesizing2-[4-{3-(dibenzofuran-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBFCzBIm-II), which is one of the carbazole derivativesdescribed in Embodiment 1, is described. A structure of DBFCzBIm-II isillustrated in the following structural formula (200).

First, a method of synthesizing 4-(9H-carbazol-3-yl)dibenzofuran, whichis a synthetic intermediate of DBFCzBIm-II, will be described.4-(9H-Carbazol-3-yl)dibenzofuran is a carbazole derivative representedby the following structural formula.

Step 1: Synthesis of 4-(9H-Carbazol-3-yl)dibenzofuran

Into a 200 mL three-neck flask were placed 2.0 g (8.1 mmol) of3-bromocarbazole, 1.7 g (8.1 mmol) of dibenzofuran-4-boronic acid, and150 mg (0.5 mol) of tri(ortho-tolyl)phosphine, and the air in the flaskwas replaced with nitrogen. To this mixture were added 20 mL of toluene,20 mL of ethanol, and 15 mL (0.2 mol) of an aqueous solution ofpotassium carbonate (2.0 mol/L). In the flask, the mixture was degassedby being stirred under reduced pressure. After 23 mg (0.10 mmol) ofpalladium(II) acetate was added to this mixture, the mixture wasrefluxed at 80° C. After the reflux, the mixture was cooled to roomtemperature, and then the obtained solid was collected by suctionfiltration. The collected solid was dissolved in 100 mL of toluene, andthis solution was filtered through Celite (produced by Wako PureChemical Industries, Ltd., Catalog No. 531-16855), Florisil (produced byWako Pure Chemical Industries, Ltd., Catalog No. 540-00135), andalumina. The solid obtained by concentration of the obtained filtratewas recrystallized from toluene/hexane, so that 2.3 g of a white solidwas obtained in 85% yield. The synthesis scheme of Step 1 is illustratedin the formula (a-2).

Step 2: Synthesis of2-[4-{3-(Dibenzofuran-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBFCzBIm-II)

Into a 100 mL three-neck flask were placed 0.70 g (1.0 mmol) of2-(4-bromophenyl)-3-phenylbenzimidazole and 0.67 g (1.0 mmol) of4-(9H-carbazol-3-yl)dibenzofuran, and the air in the flask was replacedwith nitrogen. To this mixture were added 15 mL of toluene, 0.10 mL oftri(tert-butyl)phosphine (a 10 wt % hexane solution), and 0.48 g (4.3mmol) of sodium tert-butoxide. This mixture was degassed while beingstirred under reduced pressure. This mixture was stirred at 110° C. for20 hours. After the stirring, the mixture was washed twice with about 30mL of water, and the mixture was separated into an organic layer and anaqueous layer. Then, the aqueous layer was subjected to extraction twicewith about 30 mL of toluene. The organic layer and the solution of theextract were combined and washed once with about 100 mL of saturatedbrine. The obtained organic layer was dried over magnesium sulfate, andthis mixture was subjected to filtration through Celite (produced byWako Pure Chemical Industries, Ltd., Catalog No. 531-16855), Florisil(produced by Wako Pure Chemical Industries, Ltd., Catalog No.540-00135), and alumina. The obtained filtrate was concentrated to givea brown solid. The obtained brown solid was purified by silica gelcolumn chromatography (a developing solvent in which the ratio of ethylacetate to toluene was 5:95), and further recrystallized fromhexane/toluene, so that 0.86 g of a pale brown solid was obtained in 71%yield. The synthesis scheme of Step 2 is illustrated in the formula(b-2).

By a train sublimation method, 854 mg of the obtained pale brown solidwas purified. Conditions for purification by sublimation were set asfollows: the pressure was 1.8 Pa, the flow rate of argon gas was 5.0mL/min, and the temperature of the heating was 290° C. Afterpurification by sublimation, 0.64 g of a pale brown solid of thesubstance which was the object of the synthesis was recovered in a yieldof 75%.

The pale brown solid after purification by sublimation was subjected tonuclear magnetic resonance (¹H NMR) spectroscopy. The measurement dataare shown below. In addition, ¹H NMR charts are shown in FIGS. 12A and12B. Note that FIG. 12B is a chart where the range of from 7 ppm to 9ppm in FIG. 12A is enlarged.

¹H NMR (CDCl₃, 300 MHz): δ=7.31-7.50 (m, 11H), 7.54-7.65 (m, 7H), 7.72(dd, J₁=1.5 Hz, J₂=7.5 Hz, 1H), 7.88 (d, J=8.7 Hz, 2H), 7.34-8.03 (m,4H), 8.22 (d, J=7.5 Hz, 1H), 8.63 (d, J=1.5 Hz, 1H)

The measurement results showed that DBFCzBIm-II, which is the carbazolederivative represented by the above structural formula (200), wasobtained.

Further, an absorption and emission spectra of DBFCzBIm-II in a toluenesolution of DBFCzBIm-II are shown in FIG. 13A, and an absorption andemission spectra of a thin film of DBFCzBIm-II are shown in FIG. 13B. Anultraviolet-visible spectrophotometer (V-550, produced by JASCOCorporation) was used for the measurements of the spectra. The spectraof the toluene solution were measured with a toluene solution ofDBFCzBIm-II put in a quartz cell. The spectra of the thin film weremeasured with a sample prepared by evaporation of DBFCzBIm-II on aquartz substrate. Note that in the case of the absorption spectrum ofthe toluene solution, the absorption spectrum obtained by subtraction ofthe absorption spectra of quartz and toluene from the measured spectrais shown in the drawing, and in the case of the absorption spectrum ofthe thin film, the absorption spectrum obtained by subtraction of thatof the quartz substrate from the measured spectra is shown in thedrawing.

FIG. 13A shows that the maximum emission wavelengths of DBFCzBIm-II in atoluene solution of DBFCzBIm-II are around 380 nm and 395 nm (at anexcitation wavelength of 340 nm), and FIG. 13B shows that the greatestemission wavelength of the thin film of DBFCzBIm-II is around 405 nm (atan excitation wavelength of 332 nm).

Further, the ionization potential of a thin film of DBFCzBIm-II wasmeasured by a photoelectron spectrometer (AC-2, produced by Riken Keiki,Co., Ltd.) in the air. The obtained value of the ionization potentialwas converted to a negative value, so that the HOMO level of DBFCzBIm-IIwas −5.71 eV. From the data of the absorption spectra of the thin filmin FIG. 13B, the absorption edge of DBFCzBIm-II, which was obtained froma Tauc plot with an assumption of direct transition, was 3.28 eV.Therefore, the optical band gap of DBFCzBIm-II in the solid state wasestimated at 3.28 eV; from the values of the HOMO level obtained aboveand this band gap, the LUMO level of DBFCzBIm-II was able to beestimated at −2.43 eV. It was thus found that DBFCzBIm-II had a wideband gap of 3.28 eV in the solid state.

Further, the oxidation and reduction characteristics of DBFCzBIm-II weremeasured. These were examined by cyclic voltammetry (CV) measurement.Note that an electrochemical analyzer (ALS model 600A or 600C, producedby BAS Inc.) was used for the measurements.

For a solution for the CV measurements, dehydrated N,N-dimethylformamide(DMF, produced by Sigma-Aldrich Inc., 99.8%, catalog No. 22705-6) wasused as a solvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄,produced by Tokyo Chemical Industry Co., Ltd., catalog No. T0836), whichwas a supporting electrolyte, was dissolved in the solvent such that theconcentration thereof was 100 mmol/L. Further, the object to be measuredwas also dissolved in the solvent such that the concentration thereofwas 2 mmol/L. A platinum electrode (a PTE platinum electrode, producedby BAS Inc.) was used as a working electrode; a platinum electrode (aVC-3 Pt counter electrode (5 cm), produced by BAS Inc.) was used as anauxiliary electrode; and an Ag/Ag⁺ electrode (an RE5 nonaqueous solventreference electrode, produced by BAS Inc.) was used as a referenceelectrode. Note that the measurements were conducted at room temperature(20° C. to 25° C.). The scan rates for the CV measurements wereuniformly set to 0.1 V/s.

In the measurements of the oxidation characteristics, scanning in whichthe potential of the working electrode with respect to the referenceelectrode was changed from 0.00 V to 1.12 V and then changed from 1.12 Vto 0.00 V was one cycle, and 100-cycle measurements were performed. Inthe measurements of the reduction characteristics, scanning in which thepotential of the working electrode with respect to the referenceelectrode was changed from −1.26 V to −2.65 V and then changed from−2.65 V to −1.26 V was one cycle, and 100-cycle measurements wereperformed. The measurement results are shown in FIGS. 20A and 20B. Notethat FIG. 20A shows a CV chart of the oxidation characteristics, andFIG. 20B shows a CV chart of the reduction characteristics.

The measurement results revealed that DBFCzBIm-II showed a propertyeffective against repetition of redox reactions between an oxidizedstate and a neutral state and repetition of redox reactions between areduced state and a neutral state, without large variations in theoxidation and reduction peaks of the oxidation and reductioncharacteristics even after the 100-cycle measurements.

Further, the HOMO and LUMO levels of DBFCzBIm-II were calculated alsofrom the CV measurement results.

First, the potential energy of the reference electrode with respect tothe vacuum level used was −4.94 eV, as determined in Example 1.

According to FIG. 20A showing the oxidation characteristics, theoxidation peak potential E_(pa) of DBFCzBIm-II was 1.04 V. In addition,the reduction peak potential E_(pc) was 0.89 V. Therefore, the half-wavepotential (intermediate potential between E_(pa) and E_(pc)) can becalculated at 0.97 V. This means that DBFCzBIm-II is oxidized by anelectric energy of 0.97 [V vs. Ag/Ag⁺], and this energy corresponds tothe HOMO level. Here, since the potential energy of the referenceelectrode, which was used in this example, with respect to the vacuumlevel is −4.94 [eV] as described above, the HOMO level of DBFCzBIm-IIwas found to be as follows: −4.94−0.97=−5.91 [eV].

Similarly, according to FIG. 20B showing the reduction characteristics,the oxidation peak potential E_(pa) of DBFCzBIm-II was −2.47 V, and thereduction peak potential E_(pc) thereof was −2.62 V. Therefore, thehalf-wave potential (intermediate potential between E_(pa) and E_(pc))can be calculated at −2.55 V. This means that DBFCzBIm-II is reduced byan electric energy of −2.55 [V vs. Ag/Ag⁺], and this energy correspondsto the LUMO level. Here, since the potential energy of the referenceelectrode, which was used in this example, with respect to the vacuumlevel is −4.94 [eV] as described above, the LUMO level of DBFCzBIm-IIwas found to be as follows: −4.94−(−2.55)=−2.39 [eV].

Example 3

In this example are described light-emitting elements using2-[4-{3-(dibenzothiophen-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBTCzBIm-II, the structural formula (100)) and2-[4-{3-(dibenzofuran-4-yl)-9H-carbazol-9-yl}phenyl]-1-phenylbenzimidazole(abbreviation: DBFCzBIm-II, the structural formula (200)), which arecarbazole compounds described in Embodiment 1, as host materials oflight-emitting layers each using an emission center substance that emitsgreen phosphorescence.

The molecular structures of organic compounds used in this example arerepresented by the structural formulae (i) to (iv), (100), and (200)below. The element structure in FIG. 1A was a structure in which theelectron-injection layer is provided between the electron-transportlayer 114 and the second electrode 104.

[Fabrication of Light-Emitting Element 1 and Light-Emitting Element 2]

First, a glass substrate 101, over which a film of indium tin oxidecontaining silicon (ITSO) was fowled to a thickness of 110 nm as thefirst electrode 102, was prepared. A surface of the ITSO film is coveredwith an insulating film, and a 2 mm square portion of the surface isexposed in order that a light-emitting area be set to 2 mm×2 mm. Inpretreatment for forming the light-emitting elements over the substrate,the surface of the substrate was washed with water and baked at 200° C.for one hour, and then a UV ozone treatment was performed for 370seconds. Then, the substrate was transferred into a vacuum evaporationapparatus where the pressure was reduced to about 10⁻⁴ Pa, vacuum bakingat 170° C. for 30 minutes was performed in a heating chamber of thevacuum evaporation apparatus, and then the substrate was cooled down forabout 30 minutes.

Then, the substrate was fixed to a holder provided in the vacuumevaporation apparatus such that the surface of the substrate 101 overwhich the ITSO film was formed faced downward.

After the pressure in the vacuum evaporation apparatus was reduced to10⁻⁴ Pa, 4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation:BPAFLP) represented by the above structural formula (i) and molybdenum(VI) oxide were co-evaporated so that the mass ratio ofBPAFLP:molybdenum oxide was 2:1; thus, the hole-injection layer 111 wasformed. The thickness thereof was set to 50 nm. Note that theco-evaporation is an evaporation method in which a plurality ofdifferent substances is concurrently vaporized from the respectivedifferent evaporation sources.

Next, BPAFLP was evaporated to a thickness of 10 nm, so that thehole-transport layer 112 was formed.

Further, for the light-emitting element 1, the light-emitting layer 113was formed over the hole-transport layer 112 in such a way thatDBTCzBIm-II, which is the carbazole derivative represented by the abovestructural formula (100) and described in Embodiment 1,4-phenyl-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine (abbreviation:PCBA1BP) represented by the above structural formula (ii), andtris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃)represented by the above structural formula (iii) were evaporated to athickness of 20 nm so that the mass ratio of DBTCzBIm-II to PCBA1BP andIr(ppy)₃ was 1:0.25:0.06, and DBTCzBIm-II and Ir(ppy)₃ were thenevaporated to a thickness of 20 nm so that the mass ratio of DBTCzBIm-IIto Ir(ppy)₃ was 1:0.06. Next, DBTCzBIm-II was evaporated to a thicknessof 15 nm, and then bathophenanthroline (abbreviation: BPhen) representedby the above structural formula (iv) was evaporated to a thickness of 15nm, so that the electron-transport layer 114 was formed.

For the light-emitting element 2, the light-emitting layer 113 wasformed over the hole-transport layer 112 in such a way that DBFCzBIm-II,which is the carbazole derivative represented by the above structuralformula (200) and described in Embodiment 1, PCBA1BP, and Ir(ppy)₃ wereevaporated to a thickness of 20 nm so that the mass ratio of DBFCzBIm-IIto PCBA1BP and Ir(ppy)₃ was 1:0.25:0.06, and DBFCzBIm-II and Ir(ppy)₃were then evaporated to a thickness of 20 nm so that the mass ratio ofDBFCzBIm-II to Ir(ppy)₃ was 1:0.06. Next, DBFCzBIm-II was evaporated toa thickness of 15 nm, and BPhen represented by the above structuralformula (iv) was evaporated to a thickness of 15 nm, so that theelectron-transport layer 114 was faulted.

Further, lithium fluoride was evaporated to a thickness of 1 nm over theelectron-transport layer 114, so that the electron-injection layer wasformed. Lastly, an aluminum film was formed to a thickness of 200 nm asthe second electrode 104 functioning as a cathode. Accordingly, thelight-emitting elements 1 and 2 were completed. Note that in the aboveevaporation processes, evaporation was all performed by a resistanceheating method.

[Operation Characteristics of Light-Emitting Elements 1 and 2]

The light-emitting elements 1 and 2 thus obtained were sealed in a glovebox under a nitrogen atmosphere without being exposed to the air. Then,the operation characteristics of these light-emitting elements weremeasured. Note that the measurements were carried out at roomtemperature (in an atmosphere kept at 25° C.).

FIG. 14 shows luminance versus current density characteristics of thelight-emitting elements, FIG. 15 shows luminance versus voltagecharacteristics thereof, and FIG. 16 shows current efficiency versusluminance characteristics thereof. In FIG. 14, the vertical axisrepresents luminance (cd/m²), and the horizontal axis represents currentdensity (mA/cm²). In FIG. 15, the vertical axis represents luminance(cd/m²), and the horizontal axis represents voltage (V). In FIG. 16, thevertical axis represents current efficiency (cd/A), and the horizontalaxis represents luminance (cd/m²).

FIG. 16 reveals the favorable luminance versus current efficiencycharacteristics of the light-emitting elements, in each of which thecarbazole derivative represented by the general formula (G1) is used forthe host material of the light-emitting layer for emitting greenphosphorescence; thus, the elements are found to be light-emittingelements having high emission efficiency. This is because each carbazolederivative represented by the general formula (G1) has a wide band gapand high triplet excitation energy, and accordingly even alight-emitting substance that emits green phosphorescence can beeffectively excited. In addition, FIG. 15 reveals the favorableluminance versus voltage characteristics of the light-emitting elements,in each of which the carbazole derivative represented by the generalformula (G1) is used for the host material of the light-emitting layerfor emitting green phosphorescence; thus, the elements are found to belight-emitting elements having low driving voltage. This indicates thateach carbazole derivative represented by the general formula (G1) has anexcellent carrier-transport property.

FIG. 17 shows emission spectra obtained when a current of 1 mA was madeto flow in the fabricated light-emitting elements 1 and 2. In FIG. 17,the vertical axis represents emission intensity (arbitrary unit), andthe horizontal axis represents wavelength (nm). The emission intensityis shown as a value relative to the greatest emission intensity assumedto be 1. FIG. 17 reveals that the light-emitting elements 1 and 2 eachemit green light that originates from Ir(ppy)₃, which was the emissioncenter substance.

Next, with an initial luminance set to 1000 cd/m², these elements weredriven under a condition where the current density was constant, andchanges in luminance with respect to the driving time were examined.FIG. 18 shows the normalized luminance versus time characteristics. FIG.18 reveals the favorable characteristics of the light-emitting elements1 and 2, and thus they are found to be light-emitting elements havinghigh reliability.

Reference Example 1

A method of synthesizing4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)(structural formula (I)) used in the above example will be specificallydescribed. A structure of BPAFLP is illustrated below.

Step 1: Method of Synthesizing 9-(4-Bromophenyl)-9-phenylfluorene

In a 100 mL three-neck flask, 1.2 g (50 mmol) of magnesium was heatedand stirred for 30 minutes under reduced pressure to be activated. Thiswas cooled to room temperature, and the flask was made to contain anitrogen atmosphere. Then, several drops of dibromoethane were added, sothat foam formation and heat generation were confirmed. To this, 12 g(50 mmol) of 2-bromobiphenyl dissolved in 10 mL of diethyl ether wasslowly added dropwise, and then the mixture was heated and stirred underreflux for 2.5 hours, so that a Grignard reagent was prepared.

Into a 500 mL three-neck flask were placed 10 g (40 mmol) of4-bromobenzophenone and 100 mL of diethyl ether. To this mixture, theGrignard reagent which was synthesized in advance was slowly addeddropwise, and then the mixture was heated and stirred under reflux for 9hours.

After reaction, this mixture solution was filtered to give a residue.The obtained residue was dissolved in 150 mL of ethyl acetate,1N-hydrochloric acid was added to the mixture until it was made acid,and the mixture was then stirred for 2 hours. The organic layer portionof this liquid was washed with water, and magnesium sulfate was addedthereto to remove moisture. This suspension was filtered, and theobtained filtrate was concentrated to give an oily substance.

Into a 500 mL recovery flask were placed this oily substance, 50 mL ofglacial acetic acid, and 1.0 mL of hydrochloric acid. The mixture wasstirred and heated at 130° C. for 1.5 hours under a nitrogen atmosphere.

After the reaction, this mixture solution was filtered to give aresidue. The obtained residue was washed with water, an aqueous solutionof sodium hydroxide, water, and methanol in this order. Then, themixture was dried, so that the substance which was the object of thesynthesis was obtained as 11 g of a white powder in 69% yield. Areaction scheme of the above synthesis method is illustrated in thefollowing scheme (J-1).

Step 2: Method of Synthesizing4-Phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP)

Into a 100 mL three-neck flask were placed 3.2 g (8.0 mmol) of9-(4-bromophenyl)-9-phenylfluorene, 2.0 g (8.0 mmol) of4-phenyl-diphenylamine, 1.0 g (10 mmol) of sodium tert-butoxide, and 23mg (0.04 mmol) of bis(dibenzylideneacetone)palladium(0), and the air inthe flask was replaced with nitrogen. Then, 20 mL of dehydrated xylenewas added to this mixture. After the mixture was degassed by beingstirred under reduced pressure, 0.2 mL (0.1 mmol) oftri(tert-butyl)phosphine (a 10 wt % hexane solution) was added to themixture. This mixture was stirred and heated at 110° C. for 2 hoursunder a nitrogen atmosphere.

After the reaction, 200 mL of toluene was added to this mixture, andthis suspension was filtered through Florisil (produced by Wako PureChemical Industries, Ltd., Catalog No. 540-00135), Celite (produced byWako Pure Chemical Industries, Ltd., Catalog No. 531-16855), andalumina. The obtained filtrate was concentrated, and the resultingsubstance was purified by silica gel column chromatography (a developingsolvent in which the ratio of toluene to hexane was 1:4). The obtainedfraction was concentrated, and acetone and methanol were added to themixture. The mixture was irradiated with ultrasonic waves and thenrecrystallized, so that the substance which was the object of thesynthesis was obtained as 4.1 g of a white powder in 92% yield. Areaction scheme of the above synthesis method is illustrated in thefollowing scheme (J-2).

The Rf values of the substance that was the object of the synthesis,9-(4-bromophenyl)-9-phenylfluorene, and 4-phenyl-diphenylamine wererespectively 0.41, 0.51, and 0.27, which were found by silica gel thinlayer chromatography (TLC) (a developing solvent in which the ratio ofethyl acetate to hexane was 1:10).

The compound obtained in Step 2 above was subjected to nuclear magneticresonance (NMR) spectroscopy. The measurement data are shown below. Themeasurement results indicate that the obtained compound was BPAFLP,which is a fluorene derivative.

¹H NMR (CDCl₃, 300 MHz): δ (ppm)=6.63-7.02 (m, 3H), 7.06-7.11 (m, 6H),7.19-7.45 (m, 18H), 7.53-7.55 (m, 2H), 7.75 (d, J=6.9, 2H).

This application is based on Japanese Patent Application serial no.2010-267060 filed with the Japan Patent Office on Nov. 30, 2010, theentire contents of which are hereby incorporated by reference.

1. A carbazole compound represented by a general formula (G1):

wherein: R¹ to R⁴ separately represent any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, a phenyl group, and a tolyl group; R⁵represents an aryl group having 6 to 12 carbon atoms; R⁶ to R¹³separately represent any one of hydrogen, an alkyl group having 1 to 4carbon atoms, and an aryl group having 6 to 12 carbon atoms; Phrepresents a substituted or unsubstituted phenylene group; and Xrepresents a sulfur atom or an oxygen atom.
 2. The carbazole compoundaccording to claim 1, wherein a substituent of the substituted phenylenegroup is an alkyl group having 1 to 4 carbon atoms.
 3. The carbazolecompound according to claim 1, wherein R⁶ to R¹³ separately representany one of a phenyl group, a naphthyl group, a biphenyl group, and atolyl group.
 4. The carbazole compound according to claim 1, wherein R⁵represents any one of a phenyl group, a naphthyl group, a biphenylgroup, and a tolyl group.
 5. The carbazole compound according to claim1, wherein the carbazole compound is represented by a general formula(G2):


6. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G3):


7. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G4):


8. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G5):


9. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G6):


10. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G7):


11. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G8):


12. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G9):


13. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G10):


14. The carbazole compound according to claim 1, wherein the carbazolecompound is represented by a general formula (G11):


15. An organic semiconductor material comprising the carbazole compoundaccording to claim
 1. 16. A light-emitting element material comprisingthe carbazole compound according to claim
 1. 17. A light-emittingelement comprising: a pair of electrodes; and a layer containing thecarbazole compound according to claim 1 between the pair of electrodes.18. A light-emitting device comprising the light-emitting elementaccording to claim
 17. 19. An electronic device comprising thelight-emitting device according to claim
 18. 20. A lighting devicecomprising the light-emitting device according to claim 18.